I’d say, it’s your theme, but it may be a plugin causing this.

What I’d do if I was you jump into my plugins directory and rename that directory temporarily then swap out my theme for a generic theme to makes sure everything works…

If everything is normal when you do that then swap the theme back and retest.

Start bringing back the plugins one by one while testing them until you find the culprit.

Let us know if you need more help.

It’s an official WP plugin made to give time to fix broken themes to work properly with WP 5.6 and later.

Unfortunately, while the developer updated the paid version they didn’t fix this. ??