I pay for SimpleLogin and as a result get Proton Pass. I began moving to it from Bitwarden but aborted when I saw it can't manage app passwords. Basically on Android (maybe iOS too) I can sign into apps using Bitwarden.
My export/import had all data except my identities and cards. So perhaps check how your exporting/importing? I did not use automated ways I just did it manually by exporting and importing a file
Just reporting back to say that yes indeed Proton Pass can fill app credentials in too. I have no idea why it didn't work when I tried it last month. I was trying it out as my Bitwarden subscription was due for renewal and I was seeing if it was worth migrating to Proton Pass. Sadly my renewal has come and gone now so will now be something I need to revisit next year.
Anyway, thank you for confirming that I was indeed incorrect.