unable to mount NFS share

I have 2 ubuntu 20.04 server and I can not mount an exported nfs dir.

NFS Server is up and running.

● nfs-server.service - NFS server and services
 Loaded: loaded (/lib/systemd/system/nfs-server.service; enabled; vendor preset: enabled)
Drop-In: /run/systemd/generator/nfs-server.service.d
         └─order-with-mounts.conf
 Active: active (exited) since Thu 2021-09-02 14:46:05 CEST; 7min ago
Process: 2374 ExecStartPre=/usr/sbin/exportfs -r (code=exited, status=0/SUCCESS)
Process: 2375 ExecStart=/usr/sbin/rpc.nfsd $RPCNFSDARGS (code=exited, status=0/SUCCESS)

Here my exports file

/_www/mydir xx.xx.24.19(rw,no_root_squash,no_subtree_check,crossmnt,async)
/_www/mydir xxxx:1cc0::19(rw,no_root_squash,no_subtree_check,crossmnt,async)

..

showmount -e localhost
Export list for localhost:
/_www/mydir xxxx:1cc0::19,xx.xx.24.19

On the client I see the open NFS ports on my server

Starting Nmap 7.80 ( https://nmap.org ) at 2021-09-02 14:58 CEST
Nmap scan report for aa (xx.xx.24.21)
Host is up (0.00018s latency).
Other addresses for www (not scanned): xxxx:xxxx::21
rDNS record for xx.xx.24.21: www.example.at
Not shown: 993 filtered ports
PORT     STATE SERVICE
22/tcp   open  ssh
25/tcp   open  smtp
80/tcp   open  http
111/tcp  open  rpcbind
443/tcp  open  https
2049/tcp open  nfs
5666/tcp open  nrpe

But when I try to mount this share I get a timeout error

mount -t nfs xx.xx.24.21:/_www/mydir /mnt/mydir
mount.nfs: Connection timed out

Additionally I turned off firewall for my test. But that did not change anything.

All tests on both machines were run as root.

I dont have any idea what is wrong.