Hi Shane, thank you for the insight.
Both my mbp and ultrafine 5K displays are calibrated monthly using a Spyder5, so their colours should be accurate or close enough.
From what I understood, researching for a few days now, is that Premiere, VLC & Firefox (among others) are simply not managing wide gamut P3 colours correctly and show over saturated/contrasted images.
Other programs, like Lightroom, Photoshop, Chrome, Quicktime, etc. all show the “correct” colours for P3 displays (aside from minor differences I don’t really care about, they are close enough for me, each software is different, so be it).
This results in exports being grossly under saturated/contrasted for anyone but P3 displays owners using VLC or Firefox… Not a big crowd !
FCPX and Resolve do manage P3 correctly from what I’ve seen / researched.
FCPX just does it “out of the box” and there’s a thing to toggle on in Resolve.
Hope it helps others,
Cheers !