Would 99% of people on 99% of tvs not be able to tell any difference? Probably.
Services like Apple TV+ do pretty well on 4K when it's their own flagship content, but none of them care about movies that were shot before digital. They'll serve a terrible automatic encoding that loses all the detail from the original film.
I just bought Lynch's "Lost Highway" on UHD Blu-ray from the Criterion Collection, and this 1997 movie has probably never looked this good in any format. Even the original film prints shown in theatres were second-generation compared to this 4K. It's mastered from the negative and perfectly encoded to preserve the massive film grain in the indoor scenes.
That doesn't exist on 4K Blu-ray. 2160p titles use the HEVC codec in combination with discs up to 125GB in capacity to minimize the artifacts as much as possible, but they are never gone.
That's video, anyway. Both 1080p and 2160p discs usually include lossless audio tracks of at least one language. If your box uses terms like "PCM", "DTS-HD MA"/"DTS-HD Master Audio", "Dolby TrueHD", that audio track is lossless.
Uncompressed 10 bit YUV444 UHD at 3840x2160 and 60fps runs at 15gbit a second, so you aren't getting a complete compression artifact free viewing experience. The largest UHD blueray will only deliver at 1% of that speed, and if you could cache it you'd get less than a minute's worth on the disk.
Now you might think that the compression you choose is suitable, and perhaps you'd be right, but it's not 100% compression artifact free, and realistically you aren't going to be seeing uncompressed UHD outside of a broadcast facility. When I stream UHD from say a music festival, I'm compressing it for the WAN section to around 120mbits of h265 at 2160p50 (europe). Even with that level of compression (15:1) it's likely better than your UHD disk.
UHD Blu-ray players though have been out since 2016, and average prices are still hovering around $200. Sometimes you see one now around $150, so maybe prices are starting to drop.
You could blame inflation for part of that, but is it also just that far fewer of them are being sold because people aren't buying physical disks anymore? I.e. they've turned into a niche luxury item.