FYI, both VP9 and AV1 support lossless as part of their base profiles, so lossless files using those codecs should be compatible with all implementations (at least in theory). Though those profiles only support 4:2:0, so it depends on your use case if that really counts as lossless.
I struggle to think of a situation where the blur of chroma subsampling is acceptable but very high quality or prores isn't good enough, I need lossless.
4:2:0 is not lossless. 4:4:4 with quantizing down to 8-bit YCbCr isn't lossless either. But 10-bit 4:4:4 is reversible back to 8-bit RGB without loss.
There's a distinction to be made between lossless (compression) and lossless (bit depth/gamma/yadda yadda); typically the format conversion isn't considered part of the "lossy/lossless" distinction.
Definitely not something to be forgotten if you're expecting to compress lossless RGB, although this is pretty rare outside of niche-ish use cases (afaik game capture is basically the only place where people are likely to be using RGB and not YCbCr? could be wrong!)
Also (if you round correctly) there is no generation loss in the format conversion. You can round-trip between them as many times as you want and you only get the loss of the initial RGB->YCbCr.
Animation production (2D or 3D) can also have raw RGB frames.
Ah, I hadn't considered that but that totally makes sense!