Wow, that did it! Thank you so much, Prez! Since I'm new to most of this, could you explain why RewriteBase / fixed the problem?
EDIT: I just encountered another problem with the redirect.
If i go to mydomain.com it redirects me to https://www.mydomain.com which is what I want, and as I mentioned, it works to go to sub-pages from there thanks to the RewriteBase /
But if I try to go to mydomain.com/about the URL suddenly changes to the entire path to index.php in the public_html folder.
I have no idea why.
Solution: My bad, I figured it out! I had the rules at the bottom, not at the top. Once I moved them to the top directly after RewriteBase / everything works.