the proper way is to group it as 1+(-2)+3

No it isn't.

you can do it in any order

You can do it in any order anyway

left to right 1-2+3=-1+3=2

addition first 1+3-2=4-2=2

subtraction first -2+1+3=-1+3=2

right to left 3-2+1=1+1=2

What I meant with ““rule”” is the meme questions pray on people not understanding/remembering what the actual rules are

And you showed that you were one of them. Every answer you got other than 4 was wrong, because you didn't understand the rules. spoiler alert: doing it in different orders never means add brackets to it. Addition first for 10-1+1 is 10+1-1, not 10-(1+1). See previous textbook example

why “left to right” conventions exist

They exist because people like you make mistakes when you try to do it in a different order. Either learn how the rules work or stop spreading disinformation. Well, you should stop spreading disinformation regardless.