gnlrdrvo [1] filed a deletion request for protonvpn-mod-next-gtk [2]: Software abandoned by upstream - the repository cannot be accessed. Also, in the comments section, the package maintainer (which is also the owner of the software) said in April they would release huge update for Linux version and "just wait 2-3 months", but it's now September (nearly 5 months) and the package remains at the same state. They did not update the PKGBUILD or point to an accessible repository, so I think we can assume that they have abandoned this.
[1] https://aur.archlinux.org/account/gnlrdrvo/ [2] https://aur.archlinux.org/pkgbase/protonvpn-mod-next-gtk/
