I've been running role-playing games on and off for years, mostly D&D going all the way back to first edition. I was the first person in my town to get the hobby bug when I was a boy, and so I was by default the GM for my first games. It stuck.
Over the decades I've had plenty of practice, and plenty of different groups. They all seemed to enjoy themselves, so I know I can't be a bad GM. I have, however, been told by some players who've had experience of playing under different people that I could be a better GM. A particular criticism was that I didn't evoke enough emotion in my descriptions or playing of NPC's.
On the occasions I've played under other GM's I have not, on the most part, found them particularly inspiring. Certainly not people I'd want to learn from or emulate. Perhaps I just prefer GMing. Who knows?
Nowadays, I GM mostly for my kids (not a comment on the RPG hobby - it's just that all my adult gaming friends prefer strategy board games). I either use pre-made adventures or chop and change existing bits of material (dungeons, NPCs etc) into my own narratives.
I do not have the time, nor the desire to go and play under another GM in a different group. If possible, I'd rather not watch videos of other people's game sessions: if I were to do so, I'd want something that I know would be good enough to learn from, ideally specifically tailored to that end.
What other options are open to me to improve my skills? I found this question on the site, How do I learn to become a good GM? - but the answers are tailored toward novices, which I am not.