I was driving my 2024 Raptor in PNW area today in 2H because it was dry, on a highway with speed limit of 70. As I started getting close to the mountains, it got very rainy and wet. My question is that is it safe to hit the 4A button while driving 70+ mph? Also, is there a max speed for 4A or I drive 80+ if needed. Thanks
Yes, you can. By the way, 4A essentially works like AWD—you can switch between 2H and 4A at any speed. 
On Wednesday afternoon, while driving up the mountain out of Steamboat Springs, I began to lose traction in 2H. I switched to 4A while moving and didn’t encounter any further issues. I even towed a Buick SUV that struggled to get up the hill through a few inches of snow on top of ice. Honestly, that might highlight just how impressive the Baja Boss AT is rather than just the capabilities of 4A. You can run 4A continuously if you prefer; it won’t damage anything.
If it wasn’t safe, it wouldn’t allow you to do it.
2wd is ok for rain
Honestly, if you have a manual, you should refer to it. I’m not trying to be rude, but it’s the best way to get accurate information and avoid issues like damaging the synchros or anything similar.
When you switch to slippery mode, it automatically engages 4H.
Is there a difference in fuel economy?