Hello everyone. I have been into basic recording audio and basic-intermediate audio work for a few months now and I want to take it a step further.
I have intermediate knowledge of the current DAW that I am currently using (REAPER)
I have no intentions on moving platform of the DAW at the moment.
What courses, lessons, YT channel, or other sources should I start to learn about mixing (and potentially mastering)
I have access to plenty of decent plug-ins that could be useful to the mixing process as well.

 

The YT channel by excellence when it comes to Reaper is "Reaper Mania"
There's also Reaper Blog.

 

Literature.

This is the only youtube video you need unless you want to get entertained by some cool "hello how are you hope your doing marvelously well, I'am your host...blablabla"-guys.

In the comments are some pretty good recommendations too. I can only advise you to read good literature because it's still the best source for knowledge.