quadripper

TLDR: do legit riders use stationary bikes or does everyone use real bikes on trainers?

I have been riding outside for years and average about 1500 - 2000 mi/ year.
I've got a new place where I'll have enough room to have an indoor bike set up. I have my main road bike (that i don't want to have to take a wheel on/off every time i want to hop on the indoor bike) so i am planning for a separate dedicated indoor cycling setup.
I have an old bike that I could use on a trainer - but it is a 7-speed and it looks like most of the modern direct-drive trainers are designed for use with newer 11-speed bikes. So if I go for a trainer, I think I would either need to use a friction drive trainer or also buy another bike to use just on the direct-drive trainer. I'm not really interested in riding on rollers as I would prefer a relaxed (non-balancing) exercise while zoning out indoors.
Because of all that, I'm kind of leaning towards a stationary bike. The ones that I've used at the gym are typically fly-wheel friction style. But it seems like it limits the realism of the workout and it may not be able to do everything like hills and stuff.

Budget, flexible, i am imagining in the $500 - 2000 range. Anybody have any thoughts or suggestions? Can i just get a friction trainer and use my old 7-speed that fits me well? What is the longevity of that solution? Should I get a dedicated stationary bike? The extreme option would be a whole new 11-speed + direct drive trainer. I am not really interested in that right now because it would cost a lot and I have yet to see how my indoor riding habits are. I like to ride outside and i have other activities I can do if the weather is bad, so not sure if I need to go all out on this.

Thanks for the help!!