MySQL upgrading from 5.7 to 8 - Throwing strange error and won't start up
I suspect this may be caused by a bug that happens when in-line upgrades go from 5.5 to 5.6 to 5.7 then finally 8.0.

The suggestion to deal with this is to run optomize table on every single table while in version 5.7. Once the 8.0 upgrade is attmpted, it is too late because you cannot go back.

I am giving up, rebuilding this server from scratch, then install 5.7 and perform the optomize table then try the upgrade to 8.0 again.

Good thing I have another 5.7 server running and a full backup of all the data.