Using Brave Browser 1.68.134 (arm) on macOS Sequoia 15.0 DB5.
When the system is rebooted, for example doing upgrades, when the system starts up and gets to the login prompt - it appears the browser is reopened (before even entering login details) and that videos/sound is playing / resumed.
By default any video/audio playback should be paused on these kinds of reboot / reopens.