Howard Miller

The big thing is that you cannot directly upgrade to Moodle 5.0. You need to make an intermediate step. Some thought/planning is required.

This table might help... http://www.syndrega.ch/blog/#php-and-dbms-compatibility-of-major-moodle-releases

What isn't working?

Open your web browser's javascript console (F12 + 'console' tab). Reload the page. Any (red) errors?

The javascript in these editors (especially Tiny) is quite sensitive. Have you any other errors on the page - especially if you have Debugging on. That can kill the editor (but still check above)

That's not an error. There MUST be something else.

It's not the version - it's no longer installed at all. Or it is and it's not configured. If you're just using the standard stuff in Ubuntu then more likely the former.

From bitter experience, I wouldn't dream of trying to upgrade a server install. I always use the LTS versions and then, when the time comes, build a new server and swap everything over. PHP may be the least of your worries. You're quite likely to get problems with the database as well. I'm sorry - I wish I could be more optimistic.