In both the third party app that I've tried it with (Blink) and BTT itself the functionality to switch between spaces instantly w/o the animation seems to be broken under the macOS 27 DB 1. Attempting to switch doesn't have any effect at all currently.
Thanks for reporting!
Apple mentioned at WWDC that they have been working on improving the space switching animations - probably this is a side effect of that. I'll check whether it can be fixed.
//edit:
Unfortunately Apple seems to be blocking programmatically generated swipe events intentionally on macOS 27. BTT has been using such (with a very high velocity) to simulate instant space switches. I'll check whether there is another way to achieve the same now (they mentioned they have been working on improving the space switching animation speed, maybe they added some new properties to control that behavior), but there might not be.
Instant space switching is back on Golden Gate with BTT 6.571 (uploading, will be available in 10min)! Also the "Switch To Desktop X" actions now also support instant switching (experimental).