Github secrets smaller than 64kb not being saved

I wanted to save the contents of an .env / .env.local file for my Symfony app as secrets, and according to the documentation it should be fine for secrets of <64 KB. My .env is 51 KB so why do I get an error message stating “Failed to add secret. Value is too large.” when I try to save it?

Thanks in advance.

EDIT

After trial-and-error, it seems having 47.953 characters (lorem ipsum) / ~47 KB or more will fail.