VPN connection to nextcloud (Linuxmint)

Good Morning!

I have recently created a Nextcloud server locally on a Raspberry Pi thanks to the Nextcloudpi iso. To access my Nextcloud outside my house I have set up a WireGuard VPN. It works perfectly on my phone where I am able to connect remotly without any problem (with Wi-Fi or 4G).

But when it comes to my computer (running on Linux Mint 20.1 Cinnamon), after having set up the VPN, I can’t connect… When I try to connect to the IP address of the server (while connected by VPN) I receive the following message: " This site is inaccessible
http://..*.**/ is inaccessible. ERR_ADDRESS_UNREACHABLE"

After switching from Firefox to chromium, I know that the problem doesn’t come from the browser…
And I have even tried to connect to the internet through my phone (shared connection) with the phone VPN activated only, and while I’m still able to connect to the server with my phone, I am still not on my computer…

So now, I am a bit lost… ^^’
Could the problem come from my firewall (since the server doesn’t have a HTTPS certificate)?
If you have any idea, I would be glad if you could help me…

Thanks in advance