Same problem on Pixel 4a5G and Firefox. The biometrics auth dialog pops up but neither of my two fingerprints works. This is the only app that shows this behavior. I end up logging in through the app directly. Overall, LP and FF support is pretty awful.
Thanks. I reconfirmed by enabling LastPass again (have since moved away to a competitor simply because of the lack of this feature), and you’re right. The auto fill API they are using is still the Android 8 API with the drop down.
Android 11’s keyboard based auto fill is better because it seems to solve the issue of the drop down not showing up often. Even though keyboards can sometimes fail to pop up when a user clicks on an input field, it still tends to be more reliable than the auto fill pop-up of Android 8.