Oh! Yes! I should have reported back - sorry!
It works great for large dogs on my 2-step foundations. I have been including links back here on all my new 2-step foundation builds.

@CatherineTCJD @Softlism @simsfreq @BellaDovah and others who are wondering about the conflict with Rebecah's toddler/puppy/kitten mods...

The conflict between Rebecah's Straight Stair Global mod and the Stair Straight Mod can be resolved by making Rebecah's mod load after simler90's. The only difference between them is that Rebecah enables the interaction for babies and up, and simler90 for children and up, so that one's very easy to overcome.

The other conflict, between Rebecah's Modular Stair Global mod and the Stair Modular Pets Fix, is a bit larger and can't be solved by load order:
If simler90's mods load last (which would be the default order with no changes to the filenames), then toddlers and puppies/kittens will be exempt from using modular and spiral stairs.
If Rebecah's mods load last, then large dogs can't walk up 2-step foundations.

Experiencing the same conflicts as you all, I made an alternate version of simler90's Stair Modular Pets Fix that incorporates the features of both mods. You need to replace simler90's mod with it, and make sure it loads after Rebecah's mods, and then you should be good to go

Thanks, @LimeyYoshi, it's great to find this waiting when I come hoping for an update!

Hi! Thank you for these mods

I really appreciate that you've uploaded them as separate fixes instead of just a big, take-it-or-leave-it bundle. There are a lot of mods out there with many features and you just have to take them all because it all comes in one big file. Not everyone might need everything there is, right? I appreciate this very much.

tq..though am confused on which one can be used and which ones are the updated ones

I hated playing with normal houses because of traffic congestion. Thank you for allowing multiple sims to walk down the stairs! :luff:

Saw this mod being recommended in one of ePSYlord's builds- would have never thought to add stair mods otherwise :P But this genuinly looks real handy! Thank you for making and collecting all these mods! ^^

I'm having an issue with a multi-floor house with spiral stairs, where a child keeps getting pushed outside, through a wall, when she goes up a flight of spiral stairs and someone is standing at the top.

I have an idea for improving Modular Stairs. If the stair is occupied anywhere on its linked objects, give it a higher Portal Penalty. This is so that people use another stair next to it and don't collide. This particularly important if they are running. Usually there is more than one stair.

Would be great if your mod didn't require Apartments. The function "Portal - Should Slide" can be called conditionally. I don't know what purpose the Lua script SimOnTopOfMe serves. If it is only for spiral stairs, it could also be called conditionally if Controller - Apartments is found.

Stairs are a bit difficult to understand, and I haven't done much with them.