Sadly, Apple has just completely cut off 3rd parties from Keychain for website passwords (they can use the Keychain for their own isolated items, but can't touch any shared password data). All non-Safari browsers are affected.

Firefox on iOS a loophole for this, because it's forced to use Safari's WebView, so it gets Safari's keychain, but it can also then prompt to save in its own password sync. Far from ideal, but at least a way to escape Apple lock-in.

I don't use Keychain as I have BitWarden but, AFAIK, the only browser able to connect to Keychain is Safari, isn't it ?

I agree it's annoying, but it's also not that big of a deal. I have 200 or so passwords duplicated in both Keychain and Keepass.