Pixel 6 here. Vanilla wireguard app. It sucks the life out of my phone and nearly halves the already half-life battery (thanks Google for your crappy OEM producers!)
Thank samsung for their shitty modems in the pixels.
However, there’s going to be a large discrepancy for all devices on battery usage based on whether VPN is on wifi or cellular, and additionally when on cellular how close to the tower they are. I live near cell edge and VPN’s roast my batts on cellular no matter the make, in city it’s almost not noticeable to have VPN on. Better to use wifi when far from towers, cellular more efficient if it’s strong signal.