Is it allowed to have two close refresh rates for one resolution

[ToastyX]

That depends on the Windows version and the graphics driver. Historically, Windows would only list one of each refresh rate rounded to the nearest integer, so only the first one defined would take effect. Newer versions of Windows 10 and 11 are capable having multiple fractional refresh rates in the advanced display settings, but the graphics driver has to support the new method. NVIDIA seems to be able to do it for some refresh rates, while AMD didn't the last time I checked.

I don't understand what you're asking about DisplayID. CRU only supports DisplayID as EDID extension blocks, not standalone DisplayID blocks. You can add multiple DisplayID extension blocks with CRU, but you can only add detailed resolutions and tiled display topology data blocks. Support for more data blocks is planned for CRU 2.0.