Apple doesn't even do 200% scaling on most of their laptops by default. My 2018 15" MBP has a native resolution of 2280x1800 but the default is looks like 1680x1050 not looks like 1440x900.
Do you have difficulty viewing 1080p at 15" at 100% scaling? I found that very viewable on my old laptop so 4K at 200% should be fine. You can adjust the scaling if you're really bothered by fractional scaling. It's improved a lot too. Much better than it was in the Win 8 days.
It depends on the version of MacOS installed, it used to be the integer 2.0x scaling in the "best for display" default.
They moved to a fractional scaling default, and I seriously assume it's for short-sighted marketing reasons. 2x scaling is the sharpest & clearest - best for eyes - setting possible, and it's a shame they hide that option.
Personally I use a third party tool to keep the resolution at the 2x scaled (so 1440x900), as otherwise I get major eye strain.
Do you have difficulty viewing 1080p at 15" at 100% scaling? I found that very viewable on my old laptop so 4K at 200% should be fine. You can adjust the scaling if you're really bothered by fractional scaling. It's improved a lot too. Much better than it was in the Win 8 days.