Joomla 3.9.92 Warning: session_start(): Failed to read session data:

This is a problem with the way that IMH has configured PHP 7.3 and PHP 7.4 in Multi-PHP manager.  Inmotion support determined that the failure "Must be due to a failure in the user's scripts".  This is NOT true.  I created a new subdomain fresh and a fresh Joomla 3.9.92 install package right from joomla.org.  I could not install on IMH's PHP 7.3 or 7.4 but could install on IMH's 7.2 PHP. 

After many hours chasing on my own, comparing installed PHP packages, I was able to deduce the magic formula that allows IMH to run modern Joomla.  You must manually go into Root WHM > Software > Easy PHP 4  then customize and filter down to the PHP 7.3 (or 7.4 if that is your preference) package list.  The one I was missing was

php73-php-mysqlnd

Again, IMH support will maintain that the issue is with your site or your script.  They were not able to offer me any help even though many of the IMH 'sales' pages claim that they love Joomla and can run it well.  In recent months, it seems that we running Joomla are being shuffled out of the support queue and dismissed.  It's sad.  I love IMH in every other respect but if you are a Joomla user, I think the handwriting is on the wall that you're on your own at IMH going forward.  Sad days indeed.   I hope the above tip helps someone.