We are introducing two new limits to Notes API: the maximum note size of 100 kB and the maximum number of notes per deal as 50. The goal of the limits is to safeguard our system from potential misuse and excessive load.
Effective from: November 15, 2023
See the full post in our Changelog
Do these limits also apply to users in the UI? And if we have 50 notes on a deal, will deleting one of them mean we can add another via API?
Hello, @Bryan_Rogers and welcome to the community! 
The answer to both of your questions is yes: these limits will also apply to users in the UI and deleting a note means that another one can be added.
Let us know if you have additional questions! 
Sincerely,
Helena