Sony a7R II vs a6400 for Artistic Street, Nature & Architecture?

Hi everyone,

I’m looking to buy my first "real" camera. I have a budget of around $600-$700. I have some experience with phone photography (iPhone 17 Pro Max) and I already use Lightroom for editing.

My main focus is Artistic Photography: Nature, Architecture, Street, and Portraits. I care more about the final "look" and resolution of the image than I do about video or high-speed sports.

I found a marketplace deal for a Sony a7R II in great condition with only 15k shutter count for $600 (body only). I could also probably find an a6400 for a similar price.

My Dilemma:

• a7R II: I love the idea of the 42.4MP full-frame sensor and IBIS for my architecture and nature shots. Since I edit in Lightroom, I feel like the extra data will be huge. But... it’s from 2015. Is it "too old" for 2026?
• a6400: I know the autofocus and tech are much newer and faster. It's smaller for the street. But will I regret the smaller APS-C sensor when doing portraits and high-res nature shots?

Is the a7R II still a viable "pro" choice for a beginner in 2026, or should I stick to the newer tech in the a6400?

Thanks for the help!