Your browser on your PC not being able to reach your server won’t be reflected on your server’s logs.
If you have an issue with Linux Mint, you’ll have to fix it on Linux Mint.
Within our guides that show you how to trust the Root CA on Linux there are a couple of warnings related to using flatpak apps. You should probably check that you saw those first, if you’ve taken that into account, I can suggest a couple of other things.