To answer just the simple question above.
Look to me you have an issue with the PHP version you are running with your Tiki.
From my experience look like you are running PHP8.x where your Tiki require something else.
You don’t give us any details so it is hard to tell you more.
- What Tiki version are you running ?
- What is you server (the domain used PHP version) ?
- What server (OS) are you using ?
- Do you have access to a control panel (which one) ?
- Do you have SSH access ?