Can't sign a message with bitcoin core

[LoyceV]

I don't have/use any of that stuff! I might very well be in a dead end here! Not sure yet, regarding my situation!

What's stopping you from doing this?

put Electrum on a USB-stick (or CDR), and install it on your offline node. Import privkey and sign offline.

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[darkv0rt3x]

I don't have/use any of that stuff! I might very well be in a dead end here! Not sure yet, regarding my situation!

What's stopping you from doing this?

put Electrum on a USB-stick (or CDR), and install it on your offline node. Import privkey and sign offline.

This offline node is in fact a virtual machine. And the problem is that I created this VM as a qcow2 image and created LVMs inside it, which apparently is redundant and seems that using LVM with a qcow2 image is losing all properties that qcow2 image provides (I am not sure which properties or features, I was just been told that).

And on top of that, these LVMs are LUKS encrypted, of course, so, I'm having issues to be able to mount this qcow2 image, decrypt the volumes and be able to access them with the VM off.

[dkbit98]

I don't have/use any of that stuff! I might very well be in a dead end here! Not sure yet, regarding my situation!

It's easy and cheap to buy or make your own DIY trezor hardware wallet, but I am not 100% sure it would work in your situation.
Last suggestion I have is to try using some alternative desktop wallets instead of Bitcoin Core, and you don't have many options to choose, but they are all open source.
It appears that Specter wallet is supporting signing a message from bech32 addresses, and I am not sure about Sparrow wallet, so you need to check that for yourself.

1. Specter desktop wallet:
https://specter.solutions/desktop/
https://docs.specter.solutions/desktop/sign-message/

2. Sparrow wallet:
https://sparrowwallet.com/

And on top of that, these LVMs are LUKS encrypted, of course, so, I'm having issues to be able to mount this qcow2 image, decrypt the volumes and be able to access them with the VM off.

I guess that's what you get when you complicate things to much

[LoyceV]

This offline node is in fact a virtual machine.

If the host OS is online, it's not air-gapped and I wouldn't call it a a cold wallet.

And the problem is that I created this VM as a qcow2 image and created LVMs inside it, which apparently is redundant and seems that using LVM with a qcow2 image is losing all properties that qcow2 image provides (I am not sure which properties or features, I was just been told that).

And on top of that, these LVMs are LUKS encrypted, of course, so, I'm having issues to be able to mount this qcow2 image, decrypt the volumes and be able to access them with the VM off.

I'm not familiar with qcow2, but it sounds like a good opportunity to start over from scratch. Or just get another VM and do the Electrum signing in there. Or use the "Shared Folders" feature (in VirtualBox) to copy Electrum from the host OS.

[darkv0rt3x]

I almost forget about this thread as I solved the problem.
I made things simpler and probably a bit more secure (removing complexity might mean being more secure)

At this point, my secure vault, which I consider air gapped (explain why later), is the following:

Create Luks encrypted container
Mount this container somewhere in my laptop
Installed Debian (GUI) on it, with encrypted partitions (also with Luks)
Installed all needed software, updates, etc
Moved all sensitive information from old VM to this new VM while host machine (my laptop) is offline. This is why I consider it air gapped. I turn off wifi while the VM is being used and PKs are in plain text, even if it's only for a second!
Removed network interface (and never add it again).
Whenever I need/want to update the software in the VM, I have 2 choices:
1 - create new VM and install latest versions and updates
2 - update packages and software knowing that this forces me to re-add network interface (not likely to happen in my case)