Edit2 (SUCCESS): First off, thank you to all who responded! I got my Plex server working perfectly. I didn't get email notifications with updates to the question for some reason so I just checked and got it all working.
@Terrance, I did manually create an actual mount point under "/media/HDD-M" (HDD-M s the drive name, HDD-Movies) through the initial guide I referenced. It did seem to work but Plex was still blind. Following that new mount point would lead me to my drive and allow access but made no difference to Plex. After following @user535733 response I realized the original guide I found may have allowed me to screw things up so I followed it backwards and undid everything before trying the link you posted @Terrance which worked after I messed with the mount point renaming a bit until Ubuntu was satisfied with my efforts. Just like that, it read and streamed without a hitch. For some reason, Ubuntu didn't like "/media/HDD-M" but once I changed it to "/media/SG" it worked without issue. No clue why that syntax made any sort of difference, but it did..
Either way, I really appreciate the assistance so much from you all. I was running Ubuntu fulltime ~13 years ago as a young nerdy kiddo and abandoned it when my mom got me a Macbook for graduating high school early so I forgot most of what I had learned. I plan on this getting me back into linux and eventually being proficient enough to help others like you all helped me.
Edit: I followed @user535733 instructions and immediately hit a wall at step 2 trying to edit permissions. I tried changing the file access to read and write and that seemed to work but had no effect on Plex. Upon trying to change the group I was modifying permissions for, a message came up stating I do not have permission to change the group.
I started off this incredibly frustrating journey a few weeks ago and came to this guide when plex couldn't see directories on my external: https://forums.plex.tv/t/using-ext-ntfs-or-other-format-drives-internal-or-external-on-linux/198544
This flew over my head very fast because of the way it was written, maybe I'm just an idiot and these steps really are perfectly formatted; but I couldn't ever get it to work at any point no matter how many times I tried.
Found AskUbuntu and looked through it which brought me to this post (plex folder access)
It was several years old which concerned me but I figured I would give it a shot. All the commands seemed to work fine but my drive is still inaccessible by Plex.
It is perfectly visible on my desktop, I understand this is a permissions issue with the way Linux is designed, not a fault of Plex or anything.
If anyone could help me out, I would really appreciate it because it's starting to drive me a bit crazy.
