So, I bought a couple different safariland ALS holsters for P226's when I used one for work. I hadnt messed with them in several years but needed an rmr compliant holster for my M&P HD 2.0 with threaded barrel. It took about 5 minutes with a dremel, another 10 minutes with a heat gun and 30 seconds with a drill to relocate one side of the thumb break. Voila! A perfect fit, it turned out really well if anyone needs to make a holster their 2.0

I've used a Safariland ALS, the basic shell and retaining system, with a cloth type shoulder holster (didn't trust the gun in a simple cloth pouch for retention or safety) and have been using it for years.
I mostly carry a 365Xl or a Shield this way.

Are you sure you don't mean SLS?

Because on a non-optic ALS holster, the ALS mechanism itself is located right where you'd need to dremel out clearance for the optic. Safariland had to redesign their ALS mechanism to mount much lower on the inside of the holster when they made the RDS compatible version of their ALS holsters.

You wouldn't be able to just carve out a chunk of an ALS holster to clear an optic without destroying the ALS retention system.

But on the SLS holsters (which are the ones with the rotating hood that look like an old school thumb break), there's no retention mechanism located inside the holster, so you can just chop a section out of the holster body with a Dremel and make it optic compatible.