I was able to load the JetBrains Mono fonts onto my iPad using AnyFont.
I downloaded the font ZIP file to iCloud Drive, added them to AnyFont, then installed them on the iPad. The detailed steps are mentioned in the 9to5Mac article.
The only (mostly) text editors I have on my iPad are Editorial and Notability. Notability let me change the font to one of the JetBrains faces but I couldn’t see them listed as options in Ediitorial.
You do need to install the profile in order to get the font loaded so yes. That being said, the app has been around for a while so I’m OK with trusting them.
I haven’t checked to see if Apple Configurator can be used to install fonts but that might be another way if folks aren’t comfortable using AnyFont or similar.