Format unsupported for random writes - RG11B10

[lingllting]

URP version: 10.4.0
Unity version: 2020.3.3
Unity uses B10G11R11_UFloatPack32 as hdr format(no alpha needed), but it seems that this format is not supported for random write.
When force the format to R16G16B16A16_SFloat, it works as expected.
But gpu overhead is huge after enabling FSR even for the performance level, the compute shader costs a large portion of the total execution time per frame. Is there any idea why this happened?