[Solved] Lost external monitor (HDMI) after clean install

[MaxFlax]

Did a clean install and used Aptik to back up and restore system
Long story may be found here:
viewtopic.php?f=46&t=353763
Sorting out some issues with Aptik, some apps did not get restored.
My main issue is that my
external monitor no longer works with Linux Mint 20.1 and (also tried an upgrade) 20.2
But, it does work with another distro on this same machine (Ubuntu Mate 20.04)

In Linux Mint - Getting messages to check your system - video drivers.
When I do this the drivers are up to date.

Saw another post mentioning similar problem, where the OP updated his kernel.
Did the same using Update Manager - 5.11.0-25
It said it updated, but nothing seemed to change.
I ran inxi, shows 5.4.0-58 (partial output below)
Checked advanced options for Linux Mint during boot, only 5.4... is shown.

Any suggestions?


inxi output

System:
Kernel: 5.4.0-58-generic x86_64 bits: 64 compiler: gcc v: 9.3.0
Desktop: Cinnamon 5.0.5 Distro: Linux Mint 20.2 Uma
base: Ubuntu 20.04 focal
Machine:
Type: Laptop System: HP product: HP Laptop 17-cp0xxx v: N/A
serial: <filter>
Mobo: HP model: 88C6 v: 74.17 serial: <filter> UEFI: AMI v: F.03
date: 03/19/2021
Battery:
ID-1: BAT0 charge: 40.3 Wh condition: 40.3/40.3 Wh (100%)
model: Hewlett-Packard Primary status: Full
Device-1: hidpp_battery_0 model: Logitech Wireless Mouse M525
charge: 100% (should be ignored) status: Discharging
CPU:
Topology: 6-Core model: AMD Ryzen 5 5500U with Radeon Graphics bits: 64
type: MT MCP arch: Zen rev: 1 L2 cache: 3072 KiB
flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3 svm
bogomips: 50307
Speed: 1397 MHz min/max: 1400/2100 MHz Core speeds (MHz): 1: 1397 2: 1397
3: 1397 4: 1395 5: 1397 6: 1398 7: 1397 8: 1395 9: 1397 10: 1397 11: 1397
12: 1397
Graphics:
Device-1: AMD vendor: Hewlett-Packard driver: N/A bus ID: 02:00.0
Display: x11 server: X.Org 1.20.9 driver: ati,fbdev
unloaded: modesetting,radeon,vesa resolution: 1600x900~77Hz
OpenGL: renderer: llvmpipe (LLVM 11.0.0 256 bits) v: 4.5 Mesa 20.2.6
direct render: Yes

[Moonstone Man]

Did the same using Update Manager - 5.11.0-25
It said it updated, but nothing seemed to change.

obQuestion: Did you reboot? If not, then do so.

You need kernel 5.11 for your machine.

[MaxFlax]

Yes, I did reboot after doing the kernel update from the update manager.
And even the advanced boot options only showed 5.4...

So, this morning I went back in an removed that latest kernel, rebooted and the reinstalled that latest kernel and rebooted again.
No joy.
This is on /dev/sda2
Let's call this my Machine Main System

Machine Other System:
I had a few empty partitions (extra space from dropping Windows, intended for future use), so I got a fresh download of Linux Mint 20.2, verified and installed in those other partitions.
To be clear this is installed on /dev/sda9
(Grub entry for this is Linux Mint 20.2 Cinnamon)
Here I was able to update the kernel and after rebooting it showed 5.11...
And, the external monitor worked just fine, oh happy day...

Then I went back into the Machine Main system /dev/sda2
this time it let me update the kernel from the Update manager.
(did this have something to do with the 20.2 install onto /dev/sda9 perhaps?)
Also, the grub menu for this Machine Main system now says Linux Mint 20.2 Uma
(after the earlier upgrade from 20.1 to 20.2 it still showed 20.1)
And, the external monitor worked just fine here also, oh happy day...
Also, there WAS a "soft popping sound" when shutting down, which I suspect was related to video drivers, it is now resolved.

The only thing I noticed, is that the update manager wants me to update the kernel
System says I'm usuing 5.11.0.25-generic
Update manager is saying to use 5.11.0.25.27-20.04.9

I assume doing this is low risk, but would like to understand the differences?

Thanks for your kindly advice and guidance.

[MaxFlax]

To tie a ribbon around this..
So I did that last kernel update proposed by the system, restarted, but update manager still shows generic, but it's not asking for another kernel update.
In any case, displays and brightness levels are back to normal.
System is running as expected, and did my backups.

To forum experts - thanks for all that you do to support us (especially those recent Linux converts like me).