Hey 😁

I don't use protean, but it is the same no matter. If the font will be self hosted, upload to storage area. Then copy the URL it produces.

Next, in style section add...

@font-face {
 font-family: "myFont";
 src: url('/s/sys_files/font.ttf');
}

So, the family name can be whatever you want to name it. The SRC URL should start with the above, replacing font.ttf with the system generated file name. Don't put the https in front, no need.

Next, goto that line in protean and add your font.

"myFont", "Helvetica Neue", sans-serif

Bingo. 😁👍