The .ttf version should be usable as-is in Godot, without any custom code. I've used it myself in both Godot 3 and 4 projects. What issues are you having?
the ttf distorts when you need to change up resolutions. Godot is very picky about that thing and requires the ".png + .fnt" file to work. In order to make it work with JSON, it needs custom code to be written in order to extract all thie data from the JSON to correctly work. Doable, but a pain to do when in need of doing something fast ^^''
import the png as font data (image font) and set the columns and rows to 16 and 8 respectively. Then set the character ranges. 0-127 if I remember correctly, but it might have been 32-127. Set the scaling to integer. I’ve been using the bitmap in Godot for a while now, it works fine. No need for the JSON at all.