I followed the directions you posted and still not working. When I change the mainwp_db_version to 8.96 and hit save it shows that is saved but when I scroll back down to see if it saved it reverts back to the old version “8.982”.
I think the same thing is happening with the “ALTER TABLE wp_mainwp_wp ENGINE = MyISAM ;” change. When I paste the change and hit save it says it saved but when I go back to see if it changed it shows the old setting “SELECT * FROM wp_mainwp_wp WHERE 1”.
This is expected behavior.
When you save the mainwp_db_version to 8.96, it will jump back up to the higher version because the Dashboard will increase it.
The table prefix wp_ may be different in your case, so you may need to change the command.
Also, in the video that’s embedded in the KB article, another method was used to change the table type that does not require entering any commands. Can you check if you have a similar method available in your hosting backend and try that?
Here is the direct link to the video: https://vimeo.com/772121720