I’m very confident that it’s either this or the restore-after-crash feature that OP is seeing. I don’t think it’s anything specific to Safari, because I have never seen Safari opened before login when it’s not my default browser.
That said, there should probably be a checkbox in system settings to disable login “prewarming”.
I actually used Chrome and Edge. Both show that problem. But the main issue is not those browser autoplaying audio and video on "restore", even though it is an issue, its the OS thinking its OK to load apps before a user authenticated itself after boot
That said, there should probably be a checkbox in system settings to disable login “prewarming”.