The footwell lights are only enabled for Model 3 configurations of Long Range and Performance. If you have a Standard Range +, you have the “partial premium” interior and the footwell lights do not work, even if present.
If you have a “premium” interior, the footwell lights should be enabled. However, the footwell lights need to be a kind of LED that is dimmable. For example, check this page of puddle and footwell lights for purchase:
Model 3 Ultra Bright LED lights Pick n Mix The footwell lights look the same but are “engineered” to handle the fade down and up of the interior lighting.l
I assume that you purchased the puddle lights and installed them in the footwell. I don’t know for sure but, I would guess the standard puddle lights don’t work reliably in the footwell because they are not designed to work there.