Actually, you don't have to rely on third party hosting at all.
Go to Custom CSS and click on Manage Custom Files. Upload your WOFF and WOFF2 font files (I assume you have appropriate rights to use these files.)
Then you can add your custom CSS:
@font-face{
font-family:"Gabriela-Italic";
src:url("https://static1.squarespace.com/static/611686940176536662089c16/t/611695e27407426b9e855e53/1628870114352/bb397cca-a87c-4199-8f2c-739e09729b8d.woff2") format("woff2"),url("https://static1.squarespace.com/static/611686940176536662089c16/t/611695e27407426b9e855e53/1628870114352/cdf54c6a-99fe-4cd4-9fbb-2d4ed1745a2c.woff") format("woff");
}
@font-face{
font-family:"Gabriela-SemiBold";
src:url("https://static1.squarespace.com/static/611686940176536662089c16/t/611695e27407426b9e855e53/1628870114352/6aa8eb6d-911f-4ce9-90ee-240046f59092.woff2") format("woff2"),url("https://static1.squarespace.com/static/611686940176536662089c16/t/611695e27407426b9e855e53/1628870114352/96c51cef-64fe-480a-8da0-e6f29e63fb02.woff") format("woff");
}
h1, h2, h3, h4, h5, h6 {
font-family: 'Gabriela-SemiBold' !important;
}
h1 em, h2 em, h3 em, h4 em, i, emphasis {
font-family: 'Gabriela-Italic' !important;
}
Replace the src:url with your account info, your WOFF and WOFF2 file names, and your font-family names. Make sure your font-family names are the same.