This bug is the same for iFrame as well as 8x8 Meeting App for Mac, both on JitSi and 8x8 domains.
If you have like 15 breakouts ( that depends on the height of the App window happens with fewer on shorter windows) and you try to click on a Participant … ) more _ button, all you see listed is 5 breakout rooms, effectively killing that button. It would be better “Send Participant To” if expands the breakout list to the left or right, and that list is scrollable.
We are working on an app where participants have to work in small groups of 2-4 for part of the meeting and that we can have a large number of breakouts.