This damage runs all across the underside of the deck at the front.

Here’s perspective on the worst part, though damage is present throughout that part of the underside of the deck.

This board will need to be replaced and there is possible damage above it

The end of the board, more damage noticed

This is combination termite/water damage. Termites do not stay low, they’ve very likely damaged some or all of the studs in this wall

More evidence of termite and water damage

These two boards are very soft and you can see all of the termite damage in between the two boards. Hard to show on camera

All of that dust/dirt is where termites have been. In between those two boards is a ton of damage. You can see damage on the sides of the boards too

More evidence of termites

More evidence of termite damage… all of this is in the furnace room BTW

This is hard to see, and hard to tell the extent from the furnace room, but dust trails and visible and damage in between the wood is very likely

Here’s termite damage that got wet. It’s not water damage

More termite damage along the base of the wall between the bathroom and furnace room

More damage in the wall between bathroom and furnace room

This board looks fairly new and is chewed up a lot. May not be a new board, hard to tell for sure. I’m not sure how much work you did with the bathroom down there