I haven't read every comment in this thread from the beginning, so maybe someone has observed this previously. If so, apologies for the repetition.

There's nothing inherent about turning that will cause a stall or spin. There's nothing inherent about deploying the spoilers that will cause a stall or spin. There's noting inherent about putting out the landing flaps that will cause a stall or spin. There's noting inherent about turning low that will cause a stall or spin. There's nothing inherent about doing them all at once that will cause a stall or spin. But, the more moving parts there are in your approach maneuvers the more attention it will take to keep everything in proper order. A few examples:

Turning below a few hundred feet presents the pilot with a very different peripheral scene because the inside wing tip traces a circle against the ground that is in the direction of travel rather than the opposite direction at higher altitudes. This tends to make it feel as though you are slipping and over-ruddering the turn can become a risk. Not a problem if you fly the airplane properly.

When you deploy the spoilers two things happen. First, you spoil the lift on the portion of the wing spanned by the spoiler (that's why they're called spoilers). This means to maintain unaccelerated flight the rest of the wing needs to produce more lift, which the pilot may compensate for by increasing angle of attack. Not a problem if you fly the airplane properly, but if you are too close to the angle of attack for stall, you can end up on the wrong side of the Cl vs alpha curve.

Second, deploying spoilers increases drag so the descent angle needs to increase to keep from bleeding off airspeed. The net effect between loss of lift and increase in drag depends a bit on the glider and the airspeed and g-load, but suffice to say that airspeed and AOA will have additional influences inflicted on them. Not a problem if you fly the airplane properly, but a bunch of rates and angles are going to change when you tug on the spoiler of flap handle.

I, for one, try not to change too many things too quickly all at once in the pattern, or if I do, I tend to push the nose over a bit in case I get distracted by, you know, looking out the window. Can you yank aggressively on all the handles at once and not create a problem? Absolutely, but it helps to pay good attention if you do.

The FAA preaches stabilized approach for a reason:

https://www.faa.gov/news/safety_brie...opic_16-11.pdf

Andy Blackburn
9B