I have recently had reason to subset fonts manually and I found a tool called glyphhanger which subsets arbitrary fonts to arbitrary codepoints.
As with many of the cool, useful tools on the internet these days, it's something that Zach Leatherman built. Thanks Zach!
The thing - though - is that glyphhanger requires Puppeteer.
I use Windows for all my day-to-day programming outside work, but I use Linux - via WSL2 - to actually make it a usable environment.
Puppeteer doesn't work out of the box in a "headless" Linux environment.
Thankfully, I found someone who had the same problem. They went through a lot more steps, so I thought I'd boil it down to just 2:
sudo apt install -y chromium-browser
sudo apt install -y libatk-adaptor