As far as I can see here OP has asked about CC 2020 not 2019, and in 2020 the "Legacy compositing" has been disabled

Please provide an actual solution since this is the most ridiclous subscription I have signed up for. C6 blows 2020 blows out of the water. Here is my system and you can see in image above that CC should be able to handle anything with the assigned RAM and GPU power.

Who ever finds this post and has same issue, I opened new one here https://community.adobe.com/t5/photoshop/photoshop-cc-2020-extremly-slow-no-solution-in-sight/m-p/11658868?page=1#M491948