Ho ho ho!
Christmas is around the corner and I started my Christmas and new year vacation.
Therefore user support is from now on suspended until mid January 2026.
Also, I strongly advise the macOS users, and especially users of Apple Silicon Macs against upgrading to macOS 26 Tahoe until further notice. Apple introduced new bugs or limitations into Tahoe’s display system, at least for Apple Silicon, the status on Intel Macs is completely unknown. This will limit the maximum achievable framerate for animations or fast stimulus presentation to half the video refresh rate (or the minimum inter-stimulus-interval to twice the video refresh duration). Iow. on a 60 Hz display you can’t achieve animations with more than 30 fps, or stimulus durations shorter than 33.33 msecs! At least not with properly working, accurate, trustworthy timing and timestamping. If one disables proper Screen('Flip', ..., dontwait); timing by specifying the optional dontwaitflag as 1, one can get full performance + totally broken timing. Note that, based on my current knowledge after 10 days of investigation, this performance bug of macOS 26 will affect any vision science toolkit with proper timing and timestamping. The other toolkits with their totally broken timing on macOS in the first place, including to my knowledge all the Python based toolkits, may appear to behave correctly, but that’s just because their brokenness is triggering the same macOS behavior as using Psychtoolbox with the dontwait = 1 flag. The same is true when using an old and unsuitable Psychtoolbox 3.0.19 or earlier on macOS + Apple Silicon.
There are currently no known methods to work around this macOS 26 Tahoe bug, so not upgrading is the best course of action until further notice.
See the following thread for ongoing info in the future:
I wish you all a peaceful, stress-free and chilled out Christmas and happy new year 
-mario