This will require some customization of the theme since there is no prebuilt option to do this.
Shortly, you need to deregister font files of the theme and then load them manually or by using third party plugin
Thanks @colorlibsupport and sorry for the late reply.
I have read a bit about that, so I downloaded the fonts I need (in woff and woff2 format) and added the relevant code to my style.css).
However, gstatic is still loaded, so how do I deregister the theme’s font files? (I tried searching for a generic option to enable/disable google fonts, but did not find one).
Downloading fonts and loading them by new stylesheet will not stop fonts loading form gstatic, it’s a part of the job, now you need to find font declarations and deregister or remove them.
p.s. as I said there are no options from the theme to disable them, you need to search it in files