Both 1Password and ProtonPass password managers do not autofill login/passwords in Chrome, Brave, Opera browsers in GrapheneOS.
However, both 1Password and ProtonPass are working fine in built-in Vanadium and also in Firefox.
As this problem is the same for 2 password managers, I assume this is GrapheneOS problem.

Odd, that both 1Password and ProtonPass work in Vanadium, but do not work in other Chromium browsers (Chrome and Brave).

I read many related topics on this forum, but the posts are from 2022/2023. People said that it didn't work even in Vanadium (but worked in Firefox). To me it works in Vanadium too, but not in Brave, Chrome, Opera.
Others say that autofill works in all browsers for them.

Where working, autofill appear right near the input fields, no suggestions for password manager in the keyboard upper line.

GrapheneOS:
Settings > Passwords, passkeys & Accounts > Autofill preferred service: 1Password/ProtonPass.
1Password Settings > Autofill > All on

Sandboxed Google Play Services: tried both installed and not.

Hardware: Pixel 6a
Android version 15 (GrapheneOS)

1Password version: 8.10.56
ProtonPass version: 1.28.3