Anybody have any idea why this piston is still powered? There is not redstone power connected to directly to it, and the nearest sources are either an off torch or a repeater. If it helps I'm using minecraft version 1.16.4.
The piston receives power through quasi-connectivity from the block the torch is attached to. QC power acts upon elements that can receive it (pistons, droppers, dispensers) in situation where a block above the element in question would be activated - imagine placing a redstone lamp on top of the piston; if the lamp is lit, the piston is powered. In this case, the torch goes off after the block receives power, so the piston doesn't retract.
There's more to QC (related to block updates) but it's not relevant here. Regardless, what QC broke, QC can fix. Move your torch with all its power infrastructure a block up, and the piston will be out of range of the solid block's QC - and while it will be out of reach of the torch direct power downwards, the block space right above it won't. In other words, this works: