Thank you for your answers.

@hy:
I use an older version that doesn't use StellarSolver. The full output doesn't have any mention of number of stars found:

2021-03-24T23:06:47 Solver failed. Try again.
2021-03-24T23:06:47 Starting solver...
2021-03-24T23:06:47 Solver iteration #1
2021-03-24T23:06:47 Using solver options: -O --no-plots --no-verify --resort -3 195.41 -4 -13.3665 -5 15 -L 1.0315 -H 1.26072 -u app
2021-03-24T23:03:46 World Coordinate System (WCS) is enabled. CCD rotation must be set either manually in the CCD driver or by solving an image before proceeding to capture any further images, otherwise the WCS information may be invalid.
2021-03-24T23:03:45 Detected Astrometry.net version 0.76 2021-03-24T23:03:45 Idle.

@PDB: I am 90% sure the version I have comes from the native repos of Raspberry Pi OS. apt search kstars shows this:
kstars/stable,now 5:3.0.0-1 armhf [installed] 
desktop planetarium, observation planning and telescope control

kstars-data/stable,now 5:3.0.0-1 all [installed,automatic]  
data files for KStars desktop planetarium

I did attempt to install the nightly version on this same install but it was too buggy so I backed off. Now everything works fine except for that solver.

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