Switch crashed hard and it will not load the new firmware

Register your switch in My Netgear and open a case via Chat. This should work even after the 90d initial support as that's part of their lifetime warranty. You are stuck in u-boot and although there are likely ways for outsiders to guesstimate a way into getting either an image booted from the secondary partition I wouldn't lightheartedly mingle in U-Boot since you are still eligible to support.

If you get this fixed with their help, sharing your solution would be appreciated. Possibly they send you a new switch instead if it takes to long for them to fix this.

I could imagine that sending them outputs of the following commands including your error message might be helpful for a quicker diagnose:

• printenv
• fsinfo
• ls
• version

printenv in U-Boot gives some information about boot arguments. There are different ways within U-Boot in order to boot or load an OS in another fashion that can but don't need to be specific to this switch. This is knowledge Netgear support hopefully should have since that is specific to their switch.