

Just sharing my experience, I had the same doubt before I buy and couldn't find a definitive answer, since you find opposite answers in the same post.
Instinct 3 Solar Tactical 50mm
Glass screen protector
JSYK, I live in a very sunny place, almost the entire year. Temperatures crazy high. As usual, today was a sunny day, not too intense but totally clear skys, not even the small clouds. Both for exact 30 min, 19 min difference between the end of Test 1 and starting Test 2.
Photo 1 - Without screen protector
Started at 14:28
39.0 Lux Hours in 30min
Photo 2 - With screen protector
Started at 15:17
43.6 Lux Hours in 30min
So, it does not affect anything. Better have the screen protector. The insignificant difference of +4.6 Lux Hours might be the sun aligning better directly to the watch. It was in the exact same spot and direction.
Although it charges, I dont think its good for battery health. Might be good for some emergency, or plan B.