No internet connection through ethernet using Network Manager

Good evening everyone, I would really appreciate some help here because I am pulling my hair.

Ok, some context: I got a gamer pc, the network was working fine before a motherboard replacement. The MOBO was changed for a new one, same model. I am running Ubuntu 20.04.6 LTS and using a static ip address.

Problem: I cannot connect to the internet through a wired ethernet connection, I am using a static ip provided by my university. I have tried a dozen posts here and partially solved it to some extent.

Description: The first time I turned on the pc, my network information was still saved, as expected, but could not connect to the internet. The configuration was done using the GUI. After trying different things for some time, I decided to erase the profile and enter once again manually all the information and voila, internet access. However, after rebooting the machine just to check if it was working fine, my credentials were there but no internet connection. I had to repeat the above process to get access.

What have I tried?, I identified my ethernet name, so I edited the file /etc/netplan/01-network-manager-all.yaml to be managed by netplan with all my info, it looks similar to this.

network:
 version: 2
 renderer: networkd
 ethernets:
   eth0:
     dhcp4: no
     addresses: [172.23.207.254/20]
     gateway4: 192.168.1.1
     nameservers:
         addresses: [8.8.8.8,8.8.8.4]

After that I ran:

sudo netplan generate 
sudo netplan apply

Followed by a reboot.

And voila, internet acccess once again. However, NetworkManager is displaying some ip address, gateway, etc which do not belong to what I specified.

I think this behavior is caused becauase the file /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf is configured as follows:

[keyfile]
unmanaged-devices=*,except:type:wifi,except:type:gsm,except:type:cdma,except:type:ethernet

This mismatch is causing some problems. Because when I try to connect via ssh to my computer from my home by entering the real static ip address, it simply is not possible. No communication is possible. So, if I let netplan manage my network, I am stuck because the gaming computer has internet access but is not accessible remotely.

What do I want ? I want Network Manager to manage my network and be able to connect to the internet. Obviously, I have changed the renderer to: NetworkManager but access to the internet is not possible.

Any suggestions?, any experience with this?, I am starting to lose my temper.

Thank you very much.