For anyone who lands here looking for a table tennis app: I built one, Ping Pong Smash.
It doesn't detect strokes. On the calories question in the first post, here's what a wrist sensor can and can't measure in table tennis: https://pingpongsmash.app/guides/heart-rate-calories-table-tennis
Store: https://apps.garmin.com/apps/25c6c1b1-b88f-4f33-bd53-ea54d596ea6b
For the tennis half of this thread: I also made Tennis Smash, a Connect IQ app that keeps tennis score (points, games, sets, deuce or No-Ad, tie-breaks) and saves the match to Garmin Connect with the set scores and the points won on serve and on return. It runs on the fenix 5 Plus, fenix 6 and more than 100 other Garmin watches. If stroke recognition is what you're after, Tennis AI (mentioned above) does that. Tennis Smash keeps the score instead, and I built it to stay one press per point while covering the standard rules, which I think is the right balance for most players. Store: https://apps.garmin.com/apps/7d673782-5db4-4115-bb30-20248596b21b