I have an old Wacom Bamboo tablet and pen and a microphone. I use xournal (http://xournal.sourceforge.net) and record what I'm writing and saying using a screencasting program called vokoscreen, starting and stopping occasionally so I get a bunch of video files. I use flowblade (https://jliljebl.github.io/flowblade/) to splice these together and then use ffmpeg to compress them. I upload to YouTube, though I'm looking into also uploading to alternative sites that are accessible from within China.
Once I've got a video ready, I watch it back and type up a transcript (with timings) in LaTeX: this ensures that the splicing didn't introduce any errors (e.g. including bloopers in the final cut) and also gives students a transcript. Technically, it's not LaTeX that I write, but a shorthand I devised a few years ago which I call lazy latex (lzl). I have a Python script (available here: https://github.com/jde27/lzl) which outputs HTML from the lzl file, in particular turning tikz into embedded images and rendering maths using MathJax. Then I end up with an HTML page with the notes and the video embedded at the top.
This may sound like a big faff to set up, but once it's up and running you can record quite quickly: I made eight videos today. In the past I used this to produce a flipped lecture course on algebraic topology:
and am in the middle of doing the same for my linear algebra lectures for next term (for coronavirus-reasons)
My advice: if you're trying to produce videos like this, don't aim for perfection, trying to rerecord every little glitch. It takes long enough as it is. Only rerecord if you think your explanation is going on too long/is too complicated/is really bad/misses some really crucial point. The occasional "typo" or slip of the tongue doesn't matter too much and gives people something to ask questions about in comments.