help removing 5.4 please

5.4 messed up my sight so I installed WP Downgrade/Specific Core – knowing not tested but hopeful. I downgraded to 5.2.5 which appeared to work, and that is the core number reflected in “about WP” but the editor is still the 5.4 block editor that will not update my pages (says it has updated but actually reverts to original). I tried downgrading again, to 5.4 with same result – appears to work but not affecting the block editor that I really really want to lose forever.

The page I need help with: [log in to see the link]