Hello,
I'm also having an issue with a custom font working on mobile.
This is my site url https://cop2-testsite.squarespace.com/
And here is the CSS I have, I uploaded .TTF, woff, and wodd2 files
@font-face {
font-family: 'ACUMIN-PRO-WIDE';
src: url(https://static1.squarespace.com/static/62fcb7847067bd37796b7c2a/t/6305e1abfafd33400bc4247b/1661329835245/AcuminProWide-Semibold.ttf), url(https://static1.squarespace.com/static/62fcb7847067bd37796b7c2a/t/6305e1b24c60655c9f5b4783/1661329842127/acuminprowide-semibold-webfont.woff), url(https://static1.squarespace.com/static/62fcb7847067bd37796b7c2a/t/6305e1afc3bafe6396d97dfa/1661329839035/acuminprowide-semibold-webfont.woff2);}
h1 {
font-family: 'ACUMIN-PRO-WIDE';}
h2 {
font-family: 'ACUMIN-PRO-WIDE';}
h3 {
font-family: 'ACUMIN-PRO-WIDE';}
h4 {
font-family: 'ACUMIN-PRO-WIDE';}