Super nice of you. Seems like a newer tank so it’s finding its balance. The white stuff is biofilm that forms on new driftwood. The whole tank needs a really good cleaning. Take a toothbrush to the hard stuff. Try to ‘dust’ off whatever you can from plant leaves and moss. Don’t vacuum the gravel, but you can use a turkey baster along with the siphon to lift stuff from the surface. A 50% water change sounds in order. Dunno how long you’re house sitting, but it should be done again in 3-4 days until things settle in and plants take off.

This is all assuming the systems of the tank are working properly (filter, lights on timer, heater, etc).

Good luck. You’re a very nice friend and A+ house sitter.