Where to rent 4k Blu-Ray Discs Online?

bkeske.....thanks for the suggestion.
However, I'm looking for a service that will mail me the discs like Netflix does and that I can also return the discs by mail.

Got it. Seems that’s how Netfix started, yet, these services seem practically ‘dead’ today. I’ve pretty much resorted to streaming for everything today, but it’s rare to spend money either renting or purchasing content these days. With a Roku (or similar), I have practically anything I want at my fingertips. Dropped cable years ago. 

Interesting, it really doesn’t seem that long ago when I used to to get movies at the VCR tape rental store regularly. I sold my nice Sony VCR to my postal carrier cheap, after she inquired while chatting about delivering a bunch of new vinyl to me. She was thrilled. I guess she had many VCR tapes with children content for her kids.

I'm afraid that you're up Schitt's Creek.

A bit more of a hassle, but I buy them on eBay and then sell them when I get tired of them. Most aren’t that expensive to begin with and even if you lose money it probably won’t be more than the cost of a rental, assuming you could actually rent them. You can watch when you want and you don’t have to worry about late fees.

I'm mainly interested in new releases.  Once I see a movie, I don't ever care to see it again...which is why I don't buy movies.  I don't care to stream movies because the picture quality and audio on streaming isn't as good as a 4k disc.