Valve Index/Knuckles hardware users have reported that the left controller won't interact in-game. I have identified the issue and will work on a fix once back at work :)
In the meantime, you can roll back your version of Squingle to a previous version that has support for both Index Knuckles controllers, which I've added to a beta channel.
To access it, in Steam, go to your library, right-click on Squingle, select "Properties..." and then "BETAS". From there, use the drop-down menu to select "Beta2 - temporary roll-back for Index users".
TL:DR : Index users temporarily use the beta channel for a fix to the "left-hand-only-working" issue.
Merry Christmas!