This stringer is pulling away from the wall. A true fix would address that, first, however you can just cover it by using a piece of 1/2" round trim, painted before installing, and that way it will cover the movement away from the wall for a bit, but if the stairs subsequently move more than that, you really need to address the root cause.
Cracks opening up in the corner too. I suspect the whole stairway wasn't built strongly enough to take the pounding of people going up and down the stairs.
This. All four steps pictures have fatigue and appear to be pulling away. Maybe I am just used to nightmares, but my first instinct is to also have the foundation checked. I used to see this so much and then soon after walls start cracking.
Zymo
MS polymer
skipweasel
Flexible caulk. Choose one that's paintable, though with that degree of movement the paint won't keep up anyway.
wizoko
I’ve been on the internet long enough to use dry ramen noodles
zeecrazy
Would say caulk would be your best bet. I bet there's tons of hoe to replace old caulk videos on YouTube if it's your first diy
trinxter
Hoe diy is the best diy.
Bystandr
This stringer is pulling away from the wall. A true fix would address that, first, however you can just cover it by using a piece of 1/2" round trim, painted before installing, and that way it will cover the movement away from the wall for a bit, but if the stairs subsequently move more than that, you really need to address the root cause.
MidnightTacoTruck
Burn the house down
rjcrecraft60
Would a small piece of quarter round trim be a more permanent fix?
ProCycle
The real problem is the stairway frame is pulling away from the wall. Fix that first.
HomerSimpsonsEvilTwin
That's just the trim. Doesn't mean the frame isn't separating from the wall too, but it doesn't mean it is for sure.
ProCycle
Cracks opening up in the corner too. I suspect the whole stairway wasn't built strongly enough to take the pounding of people going up and down the stairs.
Hellstorm99
This. All four steps pictures have fatigue and appear to be pulling away. Maybe I am just used to nightmares, but my first instinct is to also have the foundation checked. I used to see this so much and then soon after walls start cracking.
ProCycle
Ooh! Good point about the foundation...
Hellstorm99