This a Mint 21 VM. I use this for compiling the gmic plugin so still on Gimp 3.0.4 but 3.0.6 probably the same.
Both Gimp and Darktable (DT) are from ubuntu PPA's and the DT shows up in Gimp preferences. Click on it to make active.
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When it does not work the cause is
Either / Or Gimp or DT are flatpak / Appimage / Snap versions.
Use to be in the past, some versions of DT and the code was not compatible with the Gimp RAW loader plugin.
As with all linux, depends on versions both program and OS.