No Sanctum Boon Vendor

The only useful screenshot there is the "after selecting room" one. And even that's not actually useful because it's the first 3 rooms only. Means nothing
The rest are worthless for this.

You are barely on first floor, Most of the time you find merchant on the second floor (After first boss - Room 8)

You sometime find a merchant toward the end of the first floor.
I don't remember seeing a merchant at the start of the floor.

*Btw a floor is the 8 room, you need to go trough 4 floor (4 boss) to finish a sanctum.

As show on the previous post picture, you can see a room reward with a merchant.
That what you look for.