Originally posted by Sℨbas11:

do I need to create a new world after every new content release?

Assuming the mod stays compatible with updates, no.
https://valheim.thunderstore.io/package/JereKuusela/Upgrade_World

Originally posted by Jarska:

new content will spawn only in areas that you have not found yet.

Point of order: 'Found' in this case means 'stepped within 500m of' which is a significant chunk of the entire space.