True story: I did get up to 11 distros recently in a multiboot setup on my Thinkpad. I used Refind for the boot manager and everything worked well.

I had:
1 - Fedora
2 - Alma Linux
3 - Anti-X
4 - Slackware
5 - ElementaryOS
6 - Linux Mint
7 - Mageia
8 - EndeavourOS
9 - PopOS
10 - Lubuntu
11 - openSUSE

I’ll probably make another run at it and try to get up to 20. I need to lay out the partitions better. I definitely need to add Void and Alpine to the list.