ALVR uses index controller emulation. The index has basic finger position sensing built into the "knuckles" controllers. ALVR emulates them and passes the finger positions to steam. I haven't tried it so don't know how VaM integrates specific finger positions in SteamVR.
There is a NEW solution, one that seems pretty good.
If you have a Quest 2/3 you can add index style finger tracking as a stick on addition to the controllers, it uses a wireless dongle on the PC.
They are reasonably priced so if you really want some "basic" finger tracking check this out,
DXP_CS1_QE2 / DXP_CS1_QE3 / DXP_CS1_QP1 This is a sensor device that can add hand tracking functionality to Meta Quest2/3/Pro controllers. It is possible to achieve hand tracking equivalent to or better than the Valve Index controller. *To avoid misunderstandings regarding product...
store.diver-x.jp
I am tempted myself but not sure I am that desperate for finger tracking.