Just recently migrated to Debian 12 on my laptop full-time. I run my own Wireguard VPN server as well and had my Windows laptop client running great on that. Basically, I just wanted to use that setup and keys the same since I know it worked.
No great UI for the WireGuard setup on Debian yet from what I can tell and NetworkManager on Gnome is meh on this. Here is how I got it working.
Get the Windows Peer Config Info
Snag the text config from the Windows client setup. Copy all the text from that [Interface] and [Peer] area and maybe you have more options that me.
Save that to a text file for Debian name it something with a .config file suffix
Import via Gnome Network Manager
Point the import from file to the vpn.config file you saved off the Windows setup.
Activating and Deactivation of VPN in Gnome
After successful import, you’ll get a quick setting up in Gnome to activate and deactivate the VPN.
I do get an error after disconnecting via the quick on/off in Gnome around “Connection Failed” but minor to have that working!