Oh, it was a multistep process...step 2, put full username in a field at https://tootfinder.ch/join.php
Ok, just did it!
"Magic word searchable found. From now on, you are indexed."
✅ (all green text btw!) ✅
✅✅✅✅✅✅✅✅✅
Wow, what a weird rabbit-hole I just ended up down.
So, the “Spread Mastodon" page (tutorial?) recommends a cool-sounding browser extension as an alternative to all those constantly-dead 'fedifinder' / Twitter-person-looker-upper-tools: the ‘Whosum Social Assistant' browser extension.
Sounds cool! Sounds like the correct solution to this problem!