2FA (TOTP) works on adguard.com, but not forum.adguard.com

I have started working on cleaning up my KeePass2 import into 1Password.

Setting up 2FA for https://adguard.com/ works perfectly, and I added the 32-character Secret into 1P.

Setting up 2FA for https://forum.adguard.com/ is working very different. That website says, "Two-step verification: Enabled (Verification code via app, Backup codes)"

The Secret is only 16 characters, and it also generated ten 9-character backup codes.

When I login to https://forum.adguard.com/, 1P fills the username and password but does not show/stop/display/ask anything about 2FA. I can see the one-time entry changing every 30 seconds.

Same problem on 2 Win 10 PCs, 1P7 the other 1P8.

Mike

1Password Version: 7.9.828 & 8.5.0
Extension Version: 2.2.3 & 2.2.3 (same?)
OS Version: Windows 10 up to date