Many of the buttons on modern mice do not work in ThinLinc, e.g. the back and forward buttons. The reason for this is the VNC protocol only supports 8 buttons, and four of them are used by the scroll wheels. An extension is needed to support more things.
Note that this might be problematic on Windows where the mouse drivers often do magical stuff for the extra buttons instead of directly passing them on to the applications.
https://www.reddit.com/r/gnome/comments/uhfvp8/comment/i7fg9yp/?utm_source=share&utm_medium=web2x&context=3
Great product! Remote-ing into a Linux VM from macOS is great, especially over fast LAN. Chiming in with lacking mouse button events, though. When I run `xev` there is nothing for forward and back button presses on my Logi M650. Button events work fine to a Windows VM on same host over RDP.
Support for more mouse buttons has now been merged upstream: https://github.com/TigerVNC/tigervnc/pull/1826