Ubuntu 20.04 bridge connection is not working

I have a network scheme, as shown in the picture. My goal is to access all my devices in the network. I don't want any NAT, as it is already under my router (which runs OpenWrt). Each device should have its IP (ideally assigned by DHCP) and should be accessible throughout the entire network.

My problem is related to the Raspberry Pi, which runs Ubuntu 20.04 (Mate). It is connected to the router via Wi-Fi, and it has an ethernet port used to connect an "embedded computer." For now, it is just another laptop where I am testing if it can reach the router or my PC. I tried to create a bridged connection for eth0 but without success.

I attempted using netplan with a static IP or with enabled DHCP.

network:
  version: 2
  renderer: NetworkManager
  ethernets:
   eth0:
     dhcp4: no
  bridges:
    br0:
      dhcp4: no
      interfaces: [eth0]
      addresses: [192.168.1.50/24]
      gateway4: 192.168.1.1
      nameservers: 
        addresses: [192.168.1.1, 8.8.8.8]

Even when I configured it with a static IP, I lost the SSH connection to the RPi, and I had to attach a monitor and keyboard to fix it.

I also tried using the NetworkManager GUI. There are tons of posts on the internet, and it looks very simple, but I must be missing something or not understanding it.

Please, can anyone help me configure it or at least show me how to diagnose the network to find out where the problem is? I am desperate because I thought it should be something simple, but I have already spent an entire day on it.

To create a bridge that behaves as you want it to here, both your ethernet and your wifi interfaces on the RPi need to be members of the bridge.

You also show an IP address of 192.168.1.112 on your RPi wifi interface, but an address of 192.168.1.50 on your bridge. The IP address on your bridge interface should be whatever IP address is compatible with your OpenWRT router.