This isn't a Selects issue. It's a quirk in how DaVinci Resolve handles folder names.
What's happening
DaVinci Resolve looks at the folder your proxy files are stored in. If that folder name ends in .RDC, Resolve assumes it's a RED camera RAW folder and starts looking for .R3D files instead of your actual .mov proxies. Since those .R3D files don't exist, you get Media Offline.
Selects is exporting the correct file path. Resolve is overriding it based on the folder name alone.
How to fix it
Rename the parent folder to remove .RDC from the end.
Before:
…/filename.RDC/filename_proxies.movAfter:
…/filename/filenmae_proxies.mov
Then re-import the footage in Selects, sync, and export to DaVinci Resolve. Your clips will link up normally.
Why do my other camera proxies work fine?
Cameras like the Canon R5C store proxies in folders without the .RDC extension, so Resolve doesn't misidentify them. The issue only happens when the folder name ends in .RDC.