My son has been doing same
The slide outside but not very good when it's raining. :(
I got a climbing arch and attachment for £40 from FB marketplace. It works a treat for when he wants to climb.
I’d get something indoors so you can redirect him to something he can climb on! We got a pikler triangle that comes with a slide (climbing steps on the other side) and it really helped x
I don’t think climbing toys are the answer because you’re just teaching them climbing is okay in the house. Just keep re directing the behaviour I think is the way forward x
Distraction is often key! Try and encourage him to come away from it and play with a toy he loves. When my son started testing boundaries, often reacting to it and telling him no a lot made him want to do it even more (like touching radiators or throwing things 😬). But if you can distract him and make him forget about it, it can help for a while! Only just this week have we turned a bit of a corner with my son stopping throwing his cup/cutlery from the table after I gave him the sternest no I could muster, but that's after a year of dealing with the behaviour 🫠😂
Taking the kids to soft play today so will tell him it OK to do it here but not at home. X
Has he got something else he can climb instead? X