Since you have a second VPN, it could be the reason for the issue. Android only allows one VPN at a time, and a VPN is the only method we can use to block apps. So, could you please try the following:
Make sure the second VPN is definitely not active;
Uninstall GlassWire;
Restart your phone;
Reinstall GlassWire and see if the issue still persists.
Forgot to say that my case is on windows, and that’s not what I ask.
My concern is, I use VPN on Windows, then I try open Glasswire > Usage > Firefox, and all of my browsing activity appear. Is that mean that my VPN fail to encrypt my connection?
But when I check with Wireshark, all connection encrypted with WireGuard and no leaks.
Can you explain what data show in Usage > Browser? Is it Local DNS Cache?