Week numbers in date picker and calendar

No, it doesnā€™t.

This depends on the underlying Calendar impementation which is FullCalendar, which does have an option for this (although I have no idea what exactly it does).

As you can in our code see this option is always hard-coded to false:
https://github.com/salesagility/SuiteCRM/search?p=1&q=weekNumbers&unscoped_q=weekNumbers

A quick non-upgrade-safe fix would be to uncomment this line here and then run Admin / Repairs / Rebuild JS.

You can also ask this kind user who recently had a very similar question to yours, to make that option configurable at the same time that he works on his own change and contributes it to core: