I want to know how will it affect my rating if i dont participate in a monthly challenge?
it won’t get changed unless you make a submission in that contest
Your rating won’t be affected as long as you don’t solve (or submit) at least one problem from the monthly challenge
If you submit one or more solutions but fail to solve any problem, you won’t appear on the ranking list for that contest - but you will still see the effect on your ranking.
The direct meaning of your statement is-
“If you have not solved at least one problem in the contest, its unrated for you.”
I think you meant to say “As long as you have no submissions in the contest, its unrated for you.”