Sysadmin

The best way is the the most optimal way for you. Some can sit and read .epub guides for hours, some can only consume video content and therefore need a Udemy class and some can only do it in a proper class with a teacher.

If you're looking for resources and short on money, most Udemy classes and books can be found on torrent trackers or Library Genesis (and if you dont mind a bit of piracy). Make sure that the resource you will be learning from also provides labs, because while theory is nice, you need to get some practice in you as well. I personally didn't study the RHCSA, I instead just tasked myself with setting up services on Linux (back when CentOS was a RHEL downstream so it was 1:1 to RHEL, but Alma/Rocky can do that for you nowadays) and picked it up as I went along. Never got the cert itself as I felt it's not worth the money but I skimmed through the dumps and had no problem answering most questions.