Alright, so here's your easy local fix - go into this directory - or wherever you have CK3 installed
C:\Program Files (x86)\Steam\steamapps\common\Crusader Kings III\game\events\dlc\ep2\
Open up this file
(preferably with a program like notepad++ where you can see which line you're at, it can be in notepad, but their UI is trickier.)
ep2_tournament_events.txt
Go to line 10717 and change the following line from this
View attachment 1271755
to this
View attachment 1271756
What you're doing here is simply making the "freak event of a quintain hitting you" way less deadlier - and instead of a 33% chance of death and 33% chance of rendering you incapable - it's roughly a 98% chance of giving you a wound instead.
This is not a perfect fix since it doesn't solve the underlying issue of AI being forced into this event, but for a local fix that simply makes your AI knights stop killing each other - it works great - they will simply wound each other instead. Death is still there - but it's a MUCH lower chance.