There is a general consensus in the open-source type community around the SIL Open Font License: https://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=OF

There is a general consensus in the open-source type community around the SIL Open Font License: https://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=OFL https://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id... It’s what most of the fonts on Google Fonts, including such widely-used families as Adobe’s Source Sans Pro and Google’s own Roboto family, are licensed under, and something I imagine the creators of Optician Sans would be comfortable with.