Not a free solution, but there is an Alfred workflow that enables searching across all the tabs of all the windows in safari. I just tried it with Safari 13 (after RecentTabList stopped working).
To use it, you have to:
- Download Alfred
- Purchase the Alfred power pack, and then
- Download/import the Search Safari And Chrome Tabs workflow.
I then modified the workflow to use control-tab as a hot key.
It's not as fast as RecentTabList was but it's way faster than searching through 4-dozen open Safari windows and doing a "search open tabs" on each one to find one of your hundred+ open tabs.