The 10-bit recording of a Sony camera is dull and cannot be converted

In that case, the video does not require conversion in the codec sense. It needs color grading to get out of log space. This can be done with a LUT to get a fast start point, or you can bare-knuckle it directly with color tools.

See this post for info on using S-Log3 in Shotcut along with links to official Sony LUTs for getting S-Log3 into Rec.709: