A couple of days ago I stumbled upon a quite nice free UI font under the SIL OFL license. It's called IBM Plex (https://en.wikipedia.org/wiki/IBM_Plex) and contains sans, serif and mono cuts. The latest TTF version is available from the AUR: ttf-ibm-plex-git. The version in the community repo is outdated. In the AUR, there is also a CFF-flavoured version: otf-ibm-plex