Is there no "expose" feature (show all tabs) in iterm2 on Big Sur?
Backstory is here: https://gitlab.com/gnachman/iterm2/-/issues/9433
I removed it because it was very slow and buggy. It was some of the oldest AppKit code I wrote, and it showed. Better alternatives are:

Global search — replaces the search feature of expose.
Open Quickly — a faster UI to jump to a tab that searches things like current directory, recent commands, etc.