So Mini2 won't connect to any wifi after I updated it to Macos15 version

Remove all add-on VPN apps, remove all add-on security apps, remove all anti-malware apps, remove all add-on cleaner apps, and restart both the Mac and the Wi-Fi router, and check again:

Failing that, see how far you can get with Wi-Fi and hardware diagnostics:

• Use Wireless Diagnostics on your Mac - Apple Support
• Use Apple Diagnostics to test your Mac - Apple Support