There is no limit hard-coded like “if (testCases.size()) > limit) blow up” in the Katalon software.
Please try creating a lot of test cases in your project yourself. Experience it! Then you will find a practical answer to your question.
As far as you count the number of Test Case’s folders on disk, and as far as you are NOT going to run it,
Dozens … no problem
Some hundreds … could be alright. But you are likely to loose controle over such a large set of codes.
Thousands … nobody has ever tried. I am not going to, of course.
If I am going to run the testcases sequentially,
Dozens … I would be able to wait for them to finish, though it may take long time — 10 minutes? 30 minutes? some hours?
Hundres … No, I can’t wait. Likely to see OutOfMemoryErrors or “Code Too Large” errors.