I saw this tweet ( https://twitter.com/gnu_texmacs/status/1251554336842407938 ) and a subsequent reply about "lagging issues". The author of that reply was asked to elaborate but never did. I believe I have the same problem, though I love TeXMacs so much that I use it anyway.

Problem description: On newer OSX systems, user experiences delay between keystrokes and their appearance on the screen. Individual keystrokes have a small but almost imperceptible lag (< 0.1 seconds). 

The problem is much worse when when actually typing. Words do not appear until the time between two consecutive keystrokes is greater than some small threshold. Thus, for instance, if I keep smearing the keyboard so that the time between two consecutive detected keystrokes stays very small, I can fill up a whole paragraph of text before it appears on the screen all at once (once I stop smearing the keys). 

In practice I do not type this fast, so typically every other word fragment appears. It is still annoying.

The above occurs on the following system:

OSX Catalina 10.15.3

MacBook Pro (16 inch, 2019)

Processor 2.6 GHz 6-core i7

Graphics Intel UHD Graphics 630 1536 MB

running TeXMacs 1.99.12

The above does not occur on the following system:

OSX High Sierra 10.13.6

MacBook Pro (15 inch, 2018)

Processor 2.2 GHz i7

Graphics Intel UHD Graphics 630 1536 MB

It may have something to do with Catalina being necessarily 64-bit. 

I'm happy to help diagnose the problem further if anyone has other questions.

Best regards,

Michael