Not many VPN providers offer dedicated Linux apps. However, these providers do offer apps for a range of Linux flavors:
Private Internet Access For Linux
Private Internet Access has dedicated clients for four Linux flavors — Ubuntu 16.04+, Mint 18+, Arch, Debian), 10 simultaneous connections, no-logs policy.
ExpressVPN App For Linux
ExpressVPN has a command-line app for Linux — but no graphical app. However, the command-line app is quite good and it’s available on 64-bit and 32-bit versions of Ubuntu, Debian, Fedora and CentOS.
AirVPN For Linux
AirVPN offers Linux apps for Debian/Unbuntu, OpenSUSE, Fedora/CentOS and Arch Linux.
Mullvad For Linux
Mullvad is has a Linux client app. I’m not sure what flavors of Linux are supported.