Thanks for the help @Jim M
To clarify for any other future person who runs into the same problem, it's Admin control Panel and then "Get Support".
Once there I was able to use the system there to convert the database to this suddenly required format, but I had to use Cpanel for the site to manually edit a file to finish the job.
No such luck with converting to InnoDB tables, apparently I'd need to contact my hosting provider for that, BUT on a whim and since I didn't have even more time to spend on this today I decided to try upgrading again and this time it worked, so apparently converting the database to sql_utf8mb4 was required but the second change was not.
Regarding whether or not removing direct support tickets is a downgrade, it most certainly is. The forums already existed, direct tickets were removed. This is a way for some of users' problems to be resolved before the actual Invision tech staff need to get around to it, by being helped (at no expense by Invision) by other users. In other words, this off-loads some presumably decent amount of technical support onto the very user base that pays for Invision to stay in business in the first place. Why doesn't Invision offer a built in discount system for forum members who actually resolve customer problems for Invision? Is their time doing Invision work for them not worth anything?
Also, now that the technical support is forums only, the help seems to be more in the flavor of, "OK, you're no expert on PHP, databases, etc, but follow these confusing and sometimes not quite right instructions in this link, and get back to us after however many hours of confusion and frustration reading through walls of text and trying to do things you've never done before if you can't figure it out." instead of actually fixing the issue for the paying customer directly.
I wish instead of the error report blasting me with a giant list of things to do myself that the Invision system just told me to go to ACP/get help and use that built in system to change the database format, as that would have been much more clear and direct help and I would have likely been able to resolve this issue weeks ago.
Also, My forums worked fine for years with the older database format, so this is a new requirement which was silently put upon us, causing some percent of us the need to make this change with no warning or knowledge how to do so.. why couldn't the system detect this beforehand and give is the fast and clear instructions for how to make the change through the "get help" system?