I, too, think this issue is pretty silly... I purchased a Pixel 7 pro recently and expected functionality to be better than my previous Xiaomi Redmi Note 9 Pro. But clearly it's not.
I also moved from Lastpass to Enpass (to have a local database), and at first I was happy with it. However, the fact that Enpass is unable to get their product to work with a major flagship phone is, frankly, unbelievable
I found this thread while setting up my phone, so here follows a NICE LONG LIST of apps that won't be autofilled:
Paypal (only fills email field, not pw - Enpass keyboard fills okay)
Instagram (only fills password - Enpass keyboard has the same issue)
TP-Link Tapo (doesn't offer to fill user/pw - keyboard also fills nothing after selecting the correct entry)
TP-Link Kasa (fills only username - keyboard doesn't Auto fill)
Community by Urbanise (fills username only - keyboard fills ok)
CubeStation (Doesn't autofill at all - keyboard only works by selecting fields*)
TeamViewer (only fills email field, keyboard works as intended)
U-TEC smart lock app (only fills email, keyboard works as intended)
PADI (diving app, works ok!)
Mirabella Genio (Doesn't work at all, won't even associate the password entry with the app. Keyboard only works by manually filling username and password from the keyboard bar)
MyNetDiary (only autofills email field, keyboard fills ok)
PIA VPN (can fill both email and pw, but only if the popup comes up by pressing in the pw field. If popup pressed while in the email field, only email is filled)
Solax Cloud (only fills email field, keyboard fills ok)
Subway (Fills okay, but doesn't save the association with the app, despite the tick box selected)
Zoom (only fills email, keyboard fills ok)
Facebook Lite Messenger (doesn't autofill anything and no pop-up. Keyboard can only fill by clicking user and pw while in the correct field).
Mi Home (Xiaomi app - only fills password, keyboard only fills by manual selection of fields)
Trello (Fills only username - keyboard only fills by manual selection of fields)
Looking forward to hearing from you soon.