Hald CLUT
The Shotcut 3D LUT filter only reads certain, usually text-based LUT formats (3dl, cube). However, many tools also offer a Hald CLUT that use a (lossless) image file. There is a python script that one can use to convert these images to a cube file: https://github.com/mikeboers/LUT-Convert
Here is a Google Drive folder of a bunch of G’MIC Hald CLUTs that have already been converted:
https://drive.google.com/drive/folders/1cBaI31TaZgj6Z7abReTEHIJPVtLqY4Dg
Here is another source: http://www.digicrea.be/picturefx/