Can't fix warped bed and first layer on my Ender 3 v2 , any advice?

I've had my printer for about a month now and already have a couple of successful, but far from perfect, prints. I upgraded some parts like metal extruder, stronger springs and I also added a BLtouch because the glass bed is pretty damn warped. I can set the edges to be at the perfect height but then the center crashes pretty hard into the nozzle, I would estimate its like a 1.5mm difference. Same goes for the corner to corner middle part on the left and right which are also 1-1.5mm closer to the nozzle. I thought maybe BLtouch will help with this but it basically did nothing, I also changed first layer settings in Cura and washed my glass bed mutliple times, changed temperatures etc. but nothing helped. All I can really do at the moment is level the bed around the center, which will leave the edges to be too far away from the nozzle and it barely sticks, I'm limited to small prints which can only stay in the center.

I checked the glass bed as well as the heating metal bed under, it seems like the metal bed is slightly warped (not sure if normal) but the glass bed is a lot more warped.

Unfortunately this is normal for this price point of machine. You can not have a high quality accurate machine for next to nothing... Start looking for a replacement glass plate that will fit, or return the printer it for a refund and buy a better quality machine.

The best way to avoid warping is to use a heated build plate. This keeps the material's temperature just below the point at which it solidifies (the glass transition temperature), keeping the material flat and bonding to the build plate. For any support, you can see here the design tips and tricks here https://globerdesign.com/