Get whichever is the cheapest bike with the groupset you want. If you’re only using it on the trainer, things like frame material or weight won’t make any difference.
I would probably buy something cheap secondhand or something new with cosmetic damage off ebay?
If I was determined to get the 105 R7000 groupset (why are you after that one?) then I might buy the groupset and put it on any old cheap bike.