In my ghostty config I use:

  scrollback-limit = 512000000
  keybind = super+f=write_scrollback_file:open

It writes it to a temporary file and then opens the file in the default text editor when I hit Cmd+F.

tmux

But there's a whole thread on other workarounds etc. Apparently it's on the roadmap.

https://github.com/ghostty-org/ghostty/issues/189