Latest post block showing error

I’m having the exact same error as wpjakarta posted, as a result of upgrading from v 4 to v 5.4. I cannot figure out a way around composing new posts.
The page I need help with is https://waplesbaptistchurch.org/

I am having the same issue with all posts after 5.4 update. Solution please?

I found a solution on this page-
https://www.ads-software.com/support/topic/read-this-first-wordpress-5-4-master-list/#post-12608712

Specifically this fix-
“Don’t Panic!

Before you go any further, make sure you’ve updated your plugins and themes to the latest versions, clear your browser’s cache and cookies and re-log in to your WordPress dashboard.

The New Editor can be disabled!

If you’re in a pinch and need the editor rolled back ASAP, please install the classic editor – www.ads-software.com/plugins/classic-editor – which will restore the old editor.”