Making objects be at size and place for every phone size

I want to ask if making all your object UI elements is a bad practise. Im currently animating a object but because its UI it lags and jitters, but if its in the scene it works great. I’ve got used to making all object UI, because that way I can set the anchors and it look good and every phone size because everything is sized propery. So my question is, how to make all my objects be in the scene(not UI) and be at the same position and size no matter the screen size, just like if they were UI elements.

This tutorial pretty much covers everything. Check it out.

there is a lot of way to do that

some people just make a root parent and scale it to the screen ratio of the phone.
by example your screen is made in a 16:9 ratio but the phone screen is 4:3, you divide by the denominator so you go from 16:9 to 5.3:3 and then scale everything in % based on that

then if all child use relative position, everything should work fine

this may look dirty on some phone. but in general its not that bad