Roth and backdoor roth deadline

Hi, this is a big confusion to me but I read roth contribution deadline is filing deadline (4/15) but backdoor roth deadline is end of the year 12/31? Is this correct. Fidelity told me backdoor roth is also 4/15 but I'm getting mixed info elsewhere.

 

I got married and no longer qualify for roth even though I did roth in 2021. Im wondering if it is too late to convert the roth to traditional, and backdoor it again to have it count towards 2021.. Thanks