Issue after doing full update

What is hosting your klipper “host” (not MCU)?

As I understand M4p manta - it’s just a 3D printer controller which will drive stepper and other hardware - in klipper word we call this a MCU (Micro Controller Unit), when you flash it with klipper firmware - it will become just execution device, it don’t store any configs, setting, etc…
MCU is just dumb device which is executing actions and communicate with klipper host thru serial connection.

Then there is another part of system where klipper main code is working, usually it can be any hardware with Linux OS system, often it’s Raspbery PI but can be any pc - in klipper word we call it “Host”, its job is to store configuration, calculating paths, driving MCUs, etc…

In your case with Manta M4P board - Your “host” can live inside of additional module for Manta M4P board and it’s called “CB1 module” - it’s a kind of Raspbery PI replacement, it should contain Linux OS and klipper “host”

Good overview of a system and all it’s parts you can pick here: Klipper Architecture / Ecosystem

So when you read something about SSH - it’s about accessing “host” system where usually klipper sources are located, where you are Building firmwares, etc…
As that host have direct connection to MCU - it can push prepared Firmware to MCU (if it’s possible), or can prepare firmware which then you manually will deliver to MCU for update.
But building and preparing of firmwares can be done in any Linux OS in any hardware.

I don’t have some specific instructions for your case, but hope I did explain what goes where and now you will have better understanding what is happening and what should be done.