so, i have just tried using the new custom fonts feature but am not convinced it's working.
I selected a TTF font on my mac that i wanted to test and followed the steps to convert using https://transfonter.org/, but when i downloaded the zip file, extracted all the files (TTF, WOFF, SVG etc) it doesn't recognise any of the generate files that were converted through transfonter.
To import a custom font you need to locate the css file of the webfont. transforter should generate one. If it still doesn't work, can you send us the zip so we can test it?