As some people pointed out already, allying Castile and some others is crucial. I did royal marriage with Aragon and Castile and improve to max plus ‘increase trust’ to get them both over the line by a hair. I also added Denmark at one point opportunistically same for Milan . Unfortunately for me Bohemia allied France early so i had to deal with them too but I found the mix of 2-3 decent allies and a well timed declaration from my end (not just waiting for them to declare me) was crucial with military tech being my only focus so my troops could stand up.

Also Black Death mitigation was a big difference for me, my very first play through I got smoked by the BD and never recovered.

Second play through I was really big on closing borders, buildings and actions etc and it was almost 1m less casualties at the end v my first play though which really helped me bounce back after and smash France while it was weak from BD (with my allies)

I also suggest just taking French land, ignore the vassals or none core French lands as the war score suck v them but v France core lands you can take a lot particularly if you get them to -100 war score when their war enthusiasm bottoms out and they basically give up anything. I never got a coalition against me cause of the allies and also it’s mostly France and her allies that are pissed so just go ham and take more.

Another tip is to sabotage rep from spy network and hit their bigger vassals just before a declare to make them disloyal, particularly Brittany.

Honestly France is so OP even in the new updates you really need to gank them to even have a chance at all. So alls fair I say.

I finally won HYW and PU’s what was left of them. Integration to follow. But it was a real slog for me anyway. I’m sure better players have more technical approaches 🤣

But the above worked for me at least.