I would really love to see a successful example of a Service Mode Switch operation work on a Dell laptop. This is the 2nd time recently that it didn’t seem to work.
Are you using the latest CSME System Tools v11 r46 ?
Maybe you don’t have a solid 1-2 connection or it came loose?
If it does connect and works, you’re not going to see an ME device/Intel(R) Management Engine Interface in the device manager.
Can you try it again, and then take a shot at dumping your full bios with fptw64 -d backup.bin in the Flash Programming Tool\WIN64 folder?
Probably headed for a hardware programmer for that W25Q128FV bios chip. This recent topic may help.
There’s a lot that’s cyan colored (microcodes) in that bios. If you have a desire to update your MC, FPT won’t work, but it would be nice to dump the whole chip.