Problem after update

You need to update CSS to use H2 not H3. There was a mix of h3/2 in 2.6 and this was made consistent in the update. There was a valid reason.

As for translations, you need to update them. Some strings have different cases/have changed.

Lost all interactivity in the backend (no setting date, no uploading images, nothing) after upgrade.

Error console also shows this error: https://www.ads-software.com/support/topic/3-0-error-option-ajax-is-not-allowed-for-select2/

Great, I assumed at least your own theme was compatible ?? Any ideas?

SebH why are you posting in non related threads? Don’t do this. Post your own.