@marwerno Sure, happy to help

I haven't seen anything in the settings menu to disable the start up sound, and some of the solutions I have found in other Opera forums look like they are outdated. It might be worth starting a new thread if the issue persists after the next update though.

I not sure what you ended up doing to disable the feature, but I found a few solutions on reddit that might work in case you're interested:

Reddit thread: https://www.reddit.com/r/operabrowser/comments/14hoo1b/disable_startup_sound_on_opera_one/

Direct solution: https://www.askvg.com/tip-disable-or-remove-opera-splash-screen-or-startup-logo/#:~:text=Launch%20Opera%20One%20web%20browser,configuration%20page%20called%20“Experiments“.&text=3.,from%20the%20drop-down%20box.