Using the word "still" there is uncalibrated. 4 hours per month is barely anything.
Imagine yourself trying to learn a real skill in that allocation of time.
If anything, you may even be reducing your tech employees' "professional development" with that metric, because I bet the average tech employee already spends greater than 4 hours per month on active learning with or without management actively allowing them.
Unfortunately, HR is in charge of 'professional development'. Noone wants to fight HR and would rather keep their cushy job, get paid and let this thing crater.
Unfortunately, that is when, as a team, you have to not classify things certain ways. Still meet your commitments, but bake in learning time. It just becomes part of what you do during the sprint. Likewise, you should not have a "testing time", "quality", or "security" budget - you just bake those into how the team operates.
We've just given up on it, I just give people tickets with stuff they want to learn about. "Oh, you want to learn Selenium, here's a ticket that has Selenium"