Transmission service beyond 100k

I searched and could not find any relevant posts. I flushed my tranny at 85k when I bought it (blackish then) - they did it twice to get the color right.

I an wondering when should I do it again - also, drain & fill Vs flush?

@alawat82 previously posted saying s/he likes to drain & fill every 30k - is there a time limit too - with pandemic it's not being driven much?

Here is some good info too - unsure if he refers to flush or not:
" transmission fluid needs to be changed when dirty; typically every 35,000-50,000 miles "