Hello @guyTux !
Thanks for reaching out!
I would recommend to you the RHEL - no cost one : https://developers.redhat.com/articles/faqs-no-cost-red-hat-enterprise-linux
Also for starting the journey of certification in RHEL , I would recommend to go with RH124 & then RH134 course offered by Red Hat learning subscription :
For any help you can reach out to firstname.lastname@example.org
If you are looking to learn, especially for certifications, always use Red Hat Enterprise Linux (RHEL). More specifically, always practice and use the EXACT version that the course and exam will be delivered on as this gives you the best chance of being familiar with all the commands and processes.
Even though there aren't significant changes in minor releases, programs do get updated and add some new features or additional options to commands. You don't want to learn to use something only to find it isn't there in the classroom environment (or even worse - the exam).
For just learning, we have a "free" overview course with videos: https://www.redhat.com/en/services/training/rh024-red-hat-linux-technical-overview?section=overview on RHEL8
There are a couple of other resources with some hands-on demos: https://www.redhat.com/en/interactive-labs/enterprise-linux
Good luck and hope this helps.