Does Motion use Motion for their own project management? Well yes, but that wasn't always the case—learn a masterful lesson as to why you shouldn't always dog food your own tool.
Would you believe that the team at Motion was split early on? Some used Asana while others used Motion.
Why wouldn't the team just force Motion on everyone? Well it started as a task manager, and it didn't have full project management capabilities early on.
So while it might be tempting to get the entire team onto Motion, it would have also put too much pressure on the product roadmap, building features they needed, over the features their customers at the time needed.
Copper is another company that experienced something similar to this, in building features for a few enterprise deals they had at the time, they ostracized 99% of their existing (and target) customer-base building features like multi-currency support.
Knowing who you're building for, who is using your product, and how your team uses the product are all key things to be aware of to prevent you from building in the wrong direction.
They are using Vite for their web app.