A possible solution would be to use the developers console, usually opened with the F5 key after enabling it in Steam's game launch options for the game. You'll have to look up how to do that though as it is more that I want to type at the moment, its easy just buiried in a Steam sub menu.

Anywya, using the devs console you open it when an event starts and type in 'devcommands' and the 'stopevent' command. it ends the event right then,

There is a mod available at https://www.nexusmods.com/valheim/mods/1507 that disables the events.

If you don't use mods then there really isn't anything you can do about them other than the console windows as they a part of the games core programming and can't be disabled permenantly without a mod.

Hope this is useful. o7