Hi @wisnia
It sounds like your world might not be compatible with v11.
Which system are you using, and which version of Foundry are you using?
This article should help you to change your Foundry version on Forge Foundry VTT version selection
Remember, after setting the Foundry version, make sure to update your systems and modules. You can do this by navigating to The Bazaar and updating the packages from the “Updates Available” button, if there are any updates.
Also make sure to Stop and Start your server from The Forge
If this does not help you solve your problem, please post a screenshot of what you are running into! I’m sure that will help to add some context. Please also check in your dev tools console (F12) to see if there are any errors there, since modules which aren’t compatible can cause issues. I recommend testing with Safe Configuration which tries to load your world without any modules enabled.
Hope that helps!