You’ll need to debug what exactly is interfering with the editor functionality. I suggest disabling all active plugins and temporarily switching to one of the default Twenty themes to check if that resolves the issue. If it does, re-activate everything one item at a time to pinpoint which one is actually the source of the issue.
Hello have a similar problem with the widgets not with pages.
With a trick, I can edit the pages. So my tip, try with right mouse button and open in new windows or tab. That works by me. However, the real problem is not solved. Is only one emergency solution.