My personal experience with direct drive trainers, in my case tacx neo2t with a 105 30-11 cassette. There's no reindexing needed. I've a trek with r8000 ultegra (rim discs, quick release) + my partner who has specialized tarmac r7000 105 with thru axle and I swap the bikes around once a day and so far I had to do zero reindexing for the trainer.
Very reassuring - I guess it might be that I'm not placing the thru axle adapters correctly onto the trainer. I'll fiddle around with the parts a bit, thanks!!