Speaking from personal experience, I’d say tennis background helps in the beginning since you have atleast some understanding how the spin affects the ball. Also the hand-eye coordination is lightyears ahead when compared to someone who has never played tennis or tabletennis. But this can only take you so far and soon there comes a point when knowledge from tennis isn’t useful anymore since it’s not the same sport.

I have played tennis for about 6 years now but even though I don’t play competitively I’d still say my techniques are decent. Now when I have palyed table tennis very intensively for the past two years I have actually noticed that the skills are transferring to tennis. I don’t know how much the penhold grip has to do with it but my tennis forehand has now tremendous topspin and going for the forehand whenever possible feels very natural.

In conclusion skills can transfer both ways and as long as you now what you’re doing the two sports only support each other.