Test results:

On KV260 Rev1 I have, 

flash-kernel (3.107ubuntu2.1) in mantic-proposed is successfully installed and was able to reboot with out an issue.
```
flash-kernel:
  Installed: 3.107ubuntu2.1
  Candidate: 3.107ubuntu2.1
  Version table:
 *** 3.107ubuntu2.1 100
        100 http://ports.ubuntu.com/ubuntu-ports mantic-proposed/main arm64 Packages
        100 /var/lib/dpkg/status
     3.104ubuntu17xlnx2 500
        500 http://oem.archive.canonical.com/updates jammy-limerick/public arm64 Packages
     3.104ubuntu17 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy-updates/main arm64 Packages
     3.104ubuntu9 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy/main arm64 Packages
ubuntu@kria:~$ cat /proc/device-tree/model
ZynqMP SMK-K26 Rev1/B/A
```

flash-kernel(3.104ubuntu18) in jammy-proposed is successfully installed and was able to reboot without an issue.
```
ubuntu@kria:~$ sudo apt policy flash-kernel
flash-kernel:
  Installed: 3.104ubuntu18
  Candidate: 3.104ubuntu18
  Version table:
 *** 3.104ubuntu18 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy-proposed/main arm64 Packages
        100 /var/lib/dpkg/status
     3.104ubuntu17xlnx2 500
        500 http://oem.archive.canonical.com/updates jammy-limerick/public arm64 Packages
     3.104ubuntu17 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy-updates/main arm64 Packages
     3.104ubuntu9 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy/main arm64 Packages
ubuntu@kria:~$ cat /proc/device-tree/model
ZynqMP SMK-K26 Rev1/B/A
```


On KD240,

flash-kernel (3.107ubuntu2.1) in mantic-proposed is successfully installed and was able to reboot with out an issue.
```
Last login: Mon Jan 22 15:43:04 UTC 2024 from 192.168.88.95 on pts/0
ubuntu@kria:~$ sudo apt policy flash-kernel
[sudo] password for ubuntu:
flash-kernel:
  Installed: 3.107ubuntu2.1
  Candidate: 3.107ubuntu2.1
  Version table:
 *** 3.107ubuntu2.1 100
        100 http://ports.ubuntu.com/ubuntu-ports mantic-proposed/main arm64 Packages
        100 /var/lib/dpkg/status
     3.104ubuntu17xlnx2 500
        500 http://oem.archive.canonical.com/updates jammy-limerick/public arm64 Packages
     3.104ubuntu17 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy-updates/main arm64 Packages
     3.104ubuntu9 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy/main arm64 Packages
ubuntu@kria:~$ cat /proc/device-tree/model
ZynqMP KD240 revA/B/1
```

flash-kernel(3.104ubuntu18) in jammy-proposed is successfully installed and was able to reboot without an issue.
```
ubuntu@kria:~$ sudo apt policy flash-kernel
[sudo] password for ubuntu:
flash-kernel:
  Installed: 3.104ubuntu18
  Candidate: 3.104ubuntu18
  Version table:
 *** 3.104ubuntu18 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy-proposed/main arm64 Packages
        100 /var/lib/dpkg/status
     3.104ubuntu17xlnx2 500
        500 http://oem.archive.canonical.com/updates jammy-limerick/public arm64 Packages
     3.104ubuntu17 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy-updates/main arm64 Packages
     3.104ubuntu9 500
        500 http://ports.ubuntu.com/ubuntu-ports jammy/main arm64 Packages
ubuntu@kria:~$ cat /proc/device-tree/model
ZynqMP KD240 revA/B/1
```

Here are the test steps I took,
1- add jammy-proposed ppa
2- install the new version of the flash-kernel (3.104ubuntu18)
3- Then do the reboot on KV260 Rev1 board. It should boot without an issue.
4- add mantic-proposed ppa
5- install the new version of flash-kernel(3.107ubuntu2.1)
6- Then do the reboot on KV260 Rev1 board. It should boot without an issue.
7- then apply the same steps [1 to 6] on KD240


It seems like the flash-kernel is booting successfully with correct device tree files on both jammy-proposed and mantic-proposed. Since I dont have access to KR260 and KV260 Rev2 boards, I will subscribe Vincent from QA to verify the new version on those boards as well. Vincent also tested the flash-kernel with their boards and it seems it is working without an issue