No Platform Tool

@SilverwebLunaElf  Both the stairs tool and the platform tool are part of the base game.
You can check if you use the Legacy Edition by checking if your pc or mac meets the system requirements: https://help.ea.com/en-us/help/the-sims/the-sims-4/the-sims-4-system-requirements/
Here you can read more about the Legacy Edition: https://help.ea.com/en-us/help/the-sims/the-sims-4/the-sims-4-legacy-edition/

To find the platforms go to the build mode and click the wall section. There you will also find the  platforms.

Have fun playing. 😉

@SilverwebLunaElf  It's definitely because you're running the Legacy Edition.  The LE doesn't get content updates, even though the game is patched, so the platforms wouldn't be available.  If you're referring to the modulare stairs update, that happened before the LE was released, when there was only one version of the game, so everyone should have it.

If you're not sure whether your computer needs the Legacy Edition, please run a dxdiag and attach it to a post (Windows):

https://help.ea.com/en-us/help/pc/how-to-gather-dxdiag-information/

or list the full specs of your Mac, including operating system, as described here:

https://answers.ea.com/t5/Technical-Issues-Mac/READ-FIRST-Sims-4-Mac-Help-Guides-and-Troubleshooting/m-p/4612396#M162

Not to be entirely rude, but I know that's a crock. I got the stairs content patch MONTHS after they did the 64-bit/Legacy Edition split, 'cuz that occurred around June of THIS YEAR for me. Only thing I can think of besides a full reinstall is to try repairing the game - IF my laptop'll cooperate - 'cuz upgrading hardware's outta the question for me. If I can't fix it and no one else has any ideas, I'll just revert to TS2 since that WILL run as I expect it to other than CAS making it crash due to an apparent lack of memory following a Windows update. I'll still read up on the Legacy Edition - maybe that'll hint at something we're all missing that'll work.

I most certainly can the next time I crank up my game, if the repair I ran on it didn't work the way I wanted it to! I didn't think of grabbing a screenshot before I shut it down earlier, so no guarantees that I'll still have the same problem, now that I've run the repair through Origin... *fingers crossed* I moused over everything, though, just 'cuz I haven't played TS4 in a while–I got so frustrated with it that I went back to TS2 for a while, so I knew there was prolly a lot that I'd been missing out on–but I never saw a platform tool. Even doing a Google search for such an image from a player who DID have it show up in their game turned up nothing, which was why I started this thread in the first place...

@SilverwebLunaElf 

https://www.pcgamer.com/you-can-finally-customize-staircases-in-the-sims-4/

dated September 5, 2019.

The Legacy Edition was released on November 12, 2019.

I don't know whether you always kept your game up to date, or you took some time off playing and came back to the pleasant surprise of modular stairs, but they were in the game before the LE existed, so the LE has that feature.  It does not contain any new content created after the LE was released, including platforms.

I dunno what's up with that, then. This game has become such a headache for one reason or another that - till last night - I hadn't bothered cranking it up since June. Months-long gaps like that started becoming more and more common after "Strangerville" dropped, but I coulda sworn I had to switch to the Legacy Edition long before November of last year.

Maybe I DID mistake when the modular stair update dropped as a result of one of those gaps between playing. At this point, I have no idea. I just know that I won't bother spending anymore money on it, even if I DO upgrade my software in the future. I'll just build like I always have since TS4 dropped, or I'll go back to TS2 for my best ideas since I have the necessary build tools in THAT iteration without having to beg and plead for them, or the things to run that version of the game so I CAN have them in TS4.