Decrease the RPM speed. INCREASE the feed rate. Cut very shallow passes. The problem is hear build up that melts the acrylic. Every flute increases heat. That’s why you need to use a 0 flit if possible. Also, downcut is the worst decision because it drives the chips down and increases the heat and melting. Fast feed speed moves the bit to cooler plastic quicker.
When I cut extruded .093” acrylic I do it with slowest speed the router will go, about 120 IPM, and 3 passes with a cheap O flute upcut bit and have excellent luck
HQMaster 1/8 Shank CNC Router... https://www.amazon.com/dp/B074R9VXKQ?ref=ppx_pop_mob_ap_share
Here’s a helpful video
I ordered these and they made easy work of the cuts I needed.
https://www.amazon.com/dp/B074R9VXKQ?psc=1&ref=ppx\_yo2ov\_dt\_b\_product\_details