Linux virtual machine network DDOS protection

I have dedicated server with installed virsh. On the server I have 5 virtual servers.

When someone DDOS attack dedicated server is everyting ok. I hardly know it's an attack. But if someone attacks the virtual server, it is not possible to load the website, database, etc. I have a firewall (UFW) on the virtual server and also on the dedicated one. I also use this script for DDOS protection on all of them. The provider also has good protection (at least they boast about it - Hetzner).

Anti DDOS script:

#!/bin/bash
### 1: Drop invalid packets ### 
/sbin/iptables -t mangle -A PREROUTING -m conntrack --ctstate INVALID -j DROP  

### 2: Drop TCP packets that are new and are not SYN ### 
/sbin/iptables -t mangle -A PREROUTING -p tcp ! --syn -m conntrack --ctstate NEW -j DROP 
 
### 3: Drop SYN packets with suspicious MSS value ### 
/sbin/iptables -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP  

### 4: Block packets with bogus TCP flags ### 
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,ACK FIN -j DROP
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,URG URG -j DROP
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,PSH PSH -j DROP
/sbin/iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL NONE -j DROP

### 5: Block spoofed packets ### 
/sbin/iptables -t mangle -A PREROUTING -s 224.0.0.0/3 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 169.254.0.0/16 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 172.16.0.0/12 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 192.0.2.0/24 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 192.168.0.0/16 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 10.0.0.0/8 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 0.0.0.0/8 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 240.0.0.0/5 -j DROP 
/sbin/iptables -t mangle -A PREROUTING -s 127.0.0.0/8 ! -i lo -j DROP  

### 6: Drop ICMP (you usually don't need this protocol) ### 
/sbin/iptables -t mangle -A PREROUTING -p icmp -j DROP  

### 7: Drop fragments in all chains ### 
/sbin/iptables -t mangle -A PREROUTING -f -j DROP  

### 8: Limit connections per source IP ### 
/sbin/iptables -A INPUT -p tcp -m connlimit --connlimit-above 111 -j REJECT --reject-with tcp-reset  

### 9: Limit RST packets ### 
/sbin/iptables -A INPUT -p tcp --tcp-flags RST RST -m limit --limit 2/s --limit-burst 2 -j ACCEPT 
/sbin/iptables -A INPUT -p tcp --tcp-flags RST RST -j DROP  

### 10: Limit new TCP connections per second per source IP ### 
/sbin/iptables -A INPUT -p tcp -m conntrack --ctstate NEW -m limit --limit 60/s --limit-burst 20 -j ACCEPT 
/sbin/iptables -A INPUT -p tcp -m conntrack --ctstate NEW -j DROP  

### 11: Use SYNPROXY on all ports (disables connection limiting rule) ### 
# Hidden - unlock content above in "Mitigating SYN Floods With SYNPROXY" section

### SSH brute-force protection ### 
/sbin/iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --set 
/sbin/iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 10 -j DROP  

### Protection against port scanning ### 
/sbin/iptables -N port-scanning 
/sbin/iptables -A port-scanning -p tcp --tcp-flags SYN,ACK,FIN,RST RST -m limit --limit 1/s --limit-burst 2 -j RETURN 
/sbin/iptables -A port-scanning -j DROP

/etc/sysctl.conf

#net.ipv4.conf.default.rp_filter=1
#net.ipv4.conf.all.rp_filter=1
net.ipv6.conf.all.forwarding=1
net.ipv4.ip_forward=1

kernel.printk = 4 4 1 7 
kernel.panic = 10 
kernel.sysrq = 0 
kernel.shmmax = 4294967296 
kernel.shmall = 4194304 
kernel.core_uses_pid = 1 
kernel.msgmnb = 65536 
kernel.msgmax = 65536 
vm.swappiness = 20 
vm.dirty_ratio = 80 
vm.dirty_background_ratio = 5 
fs.file-max = 2097152 
net.core.netdev_max_backlog = 262144 
net.core.rmem_default = 31457280 
net.core.rmem_max = 67108864 
net.core.wmem_default = 31457280 
net.core.wmem_max = 67108864 
net.core.somaxconn = 65535 
net.core.optmem_max = 25165824 
net.ipv4.neigh.default.gc_thresh1 = 4096 
net.ipv4.neigh.default.gc_thresh2 = 8192 
net.ipv4.neigh.default.gc_thresh3 = 16384 
net.ipv4.neigh.default.gc_interval = 5 
net.ipv4.neigh.default.gc_stale_time = 120 
net.netfilter.nf_conntrack_max = 10000000 
net.netfilter.nf_conntrack_tcp_loose = 0 
net.netfilter.nf_conntrack_tcp_timeout_established = 1800 
net.netfilter.nf_conntrack_tcp_timeout_close = 10 
net.netfilter.nf_conntrack_tcp_timeout_close_wait = 10 
net.netfilter.nf_conntrack_tcp_timeout_fin_wait = 20 
net.netfilter.nf_conntrack_tcp_timeout_last_ack = 20 
net.netfilter.nf_conntrack_tcp_timeout_syn_recv = 20 
net.netfilter.nf_conntrack_tcp_timeout_syn_sent = 20 
net.netfilter.nf_conntrack_tcp_timeout_time_wait = 10 
net.ipv4.tcp_slow_start_after_idle = 0 
net.ipv4.ip_local_port_range = 1024 65000 
net.ipv4.ip_no_pmtu_disc = 1 
net.ipv4.route.flush = 1 
net.ipv4.route.max_size = 8048576 
net.ipv4.icmp_echo_ignore_broadcasts = 1 
net.ipv4.icmp_ignore_bogus_error_responses = 1 
net.ipv4.tcp_congestion_control = htcp 
net.ipv4.tcp_mem = 65536 131072 262144 
net.ipv4.udp_mem = 65536 131072 262144 
net.ipv4.tcp_rmem = 4096 87380 33554432 
net.ipv4.udp_rmem_min = 16384 
net.ipv4.tcp_wmem = 4096 87380 33554432 
net.ipv4.udp_wmem_min = 16384 
net.ipv4.tcp_max_tw_buckets = 1440000 
net.ipv4.tcp_tw_recycle = 0 
net.ipv4.tcp_tw_reuse = 1 
net.ipv4.tcp_max_orphans = 400000 
net.ipv4.tcp_window_scaling = 1 
net.ipv4.tcp_rfc1337 = 1 
net.ipv4.tcp_syncookies = 1 
net.ipv4.tcp_synack_retries = 1 
net.ipv4.tcp_syn_retries = 2 
net.ipv4.tcp_max_syn_backlog = 16384 
net.ipv4.tcp_timestamps = 1 
net.ipv4.tcp_sack = 1 
net.ipv4.tcp_fack = 1 
net.ipv4.tcp_ecn = 2 
net.ipv4.tcp_fin_timeout = 10 
net.ipv4.tcp_keepalive_time = 600 
net.ipv4.tcp_keepalive_intvl = 60 
net.ipv4.tcp_keepalive_probes = 10 
net.ipv4.tcp_no_metrics_save = 1 
net.ipv4.conf.all.accept_redirects = 0 
net.ipv4.conf.all.send_redirects = 0 
net.ipv4.conf.all.accept_source_route = 0 
net.ipv4.conf.all.rp_filter = 1

Dedicate network interface:

auto lo
iface lo inet loopback
iface lo inet6 loopback

auto eno2
iface eno2 inet static
    address 11.22.33.44
    netmask 255.255.255.255
    pointopoint 11.22.33.44
    gateway 11.22.33.55

iface eno2 inet6 static
  address 1234:123:123:123::1
  netmask 128
  gateway fe80::1

auto virbr1
iface virbr1 inet static
    address 11.22.33.44
    netmask 255.255.255.255
    bridge_ports none
    bridge_stp off
    bridge_fd 0
    pre-up brctl addbr virbr1
    up ip route add 22.33.44.55/28 dev virbr1
    down ip route del 22.33.44.55/28 dev virbr1

iface virbr1 inet6 static
    address 1234:123:123:123::1
    netmask 64

Virtual server network interface (bridge):

auto lo
iface lo inet loopback

auto enp1s0
iface enp1s0 inet static
  address 22.33.44.55
  netmask 255.255.255.255
  pointtopoint 11.22.33.44
  gateway 11.22.33.44

iface enp1s0 inet6 static
  address 1234:123:123:123::100
  netmask 64
  gateway 1234:123:123:123::1

I don't know how to prevent it, the problem is that when there is an attack on a virtual server. So all other virtual ones are unusable and the main one too. When there is an attack on the main server, everything is fine and it is not possible to recognize that it is an attack (only a little). I tested this through a test DDOS.