Ever since the latest App Store update (just a few days ago) I get a flash, like an open window, but with no content, at every startup. I have confirmed that it is a Bitwarden issue by not having it start at login, and the issue goes away. MacBook Pro, 2020 M1, running Monterey 12.7.2.
Edit: Just wanted to add that this same issue is also present on my 2014 Intel Mac mini, also running Monterey 12.7.2. Again, if you quit Bitwarden and then restart it, the “window flash” happens each and every time.
App Store version just updated this morning to 2023.12.1 (16254) and the issue persists. Not really a huge deal, but more of a notification to others who may be experiencing the same momentary “flash” as Bitwarden starts up.