Thanks! It's a Phanteks' 140mm in the back as an exhaust. This one.
It was actually the only part in the whole build that came broken (RGB lit up, fan did not spin and wasn't recognized by bios) ... Amazon swapped it no big deal. But was annoying to trouble shoot if it was the fan, or the cable, or the MB header, or the fan controller etc.
Nope.
Just get the matching fan https://www.amazon.com/Phanteks-SK140-DRGB-PWM-PH-F140SK_DRGB_PWM/dp/B08C24PQHF
It was this one https://www.amazon.com/dp/B08C24PQHF?ref=ppx_pop_mob_ap_share
https://www.amazon.com/gp/product/B08C24PQHF/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
this is the one for the p500a, not sure about the 400 tho.
You could also get an AIO if you wanted instead of an air cooler. I have 1 fan pushing air out the top and 3 fans (360 AIO) pushing air out the top. (Not RGB tho I think 7 RGB fans is overkill but 4 is sick). Liquid freezer 240/280 is around $100 so near the same price as the chromax noctua air cooler and a bit more expensive than the dark rock 4 but it depends on what CPU you're getting. I probably over-cooled my case for my i5-10600k but I'm also getting a 3080 so it'll help.