Are you using an AMD card? You might run into some trouble.
Also there's a codec suppport list here: https://documents.blackmagicdesign.com/SupportNotes/DaVinci_Resolve_18_Supported_Codec_List.pdf
It says that for Windows, only 8-bit H264 is support on free. For Linux, H264 is only supported on Studio. On MacOS, it's supported on both free and Studio hence why you have no problem there.