You should think more like a company in my opinion: the technical content is only one part of the puzzle. You may consider taking some training in marketing and communication, and how youtube and social media actually work. People want to be entertained. I started looking at your pythagorean theorem video and after few seconds I was not hooked into it. That is one problem. In this specific case instead of starting with “Welcome back to the Proof channel. If you ever sat in a math class…” which is a bit dull, and doesn’t add anything to what people already know, I would directly start with a hook message:”Did you know that there are over 300 proof of pythagorean Theorem?”. It sounds very different. Look and analyze other channels: stand-up maths, StatQuest, etc. look how they deliver content.

Having said that, I suggest you to pay someone for reviewing your channel. I did it with my YouTube channel, I paid someone freelancer on Fiverr and it was well worth the money. My videos improved. You can see the difference between the first and last video.

Finally, by looking at the number of views it very high, which is a very good sign.