Eh, NO!
With RPN you start within the parentheses first and then work outwards. It is not strictly 'left to right' like in your example.
The actual problem in this expression and evaluation is not "parentheses" first so much, but a pattern recognition of the reader. How does he/she/they interpret what is written on the expression. After all mathematics are whole lots of pattern recognition, when it comes to many things, expression solving is no exception on this.
ie.
6:2(2+1)
6/2(2+1)
6/(2+1)2
Same with the -1² = -1 (as I have understood that it is now
somewhat standard form in printed math), while I doubt there is none who actually uses math as tool puts this as result when using a pen and paper with same marking on paper, in other words would use parenthesis as (-1)²=1. In the other hand this is answer logical since what it actually contains is as far as I know actually (-1)*1² as in following expression: a-(b-c)=a+(-b)+c=a+(-1)(b-c)=a+[-1b+((-1)²)c] ... which to my eyes are again one of those pesky implied multiplications btw.
..but again -1²=-1 is illogical in a way the algebra is thought in ie. with quadratic formula ... aX²+bX+c is many times written as 1X²-6X+8, where b=-6 and transferred to formula ... what should be written is actually 1X²+[(-1)6]X+8 where b=(-1)6 .... with this former "style" -1² is actually +(-1)²
summa summarum.. use your head and do test calculation(s) if context do not reveal the intended formatting ...
...it seems it is a bed time, one should not take a "quick" look of eevblog in the middle of night.