This happened around 1-2 months ago. I updated my system and the fingerprint feature for polkit prompts stopped working. I am only able to use my password now to authenticate.
Fingerprint checks for sudo still work. Any idea? Any data/logs you might need?
Linux 6.5.13-7-MANJARO #1 SMP PREEMPT_DYNAMIC x86_64 GNU/Linux
That kernel is EOL since 28 November 2023. Which suggest you aren’t up-to-date, which might have, no, probably has contributed to this.
Please, update your system and use a still-supported kernel, then see if the problem persists.
This will do you good:
If you can’t or don’t want to keep your system up-to-date, then you might be, no you’ll probably be better off using a point-release distribution, like Ubuntu.
this may help
I am running pacman -Syu regularely. And the pamac GUI also says I am up-to-date. Is there any other updating mechanism I am not aware of?
Not that I’m aware of. But your mirrors might be out of wack if you don’t get errors. Try updating them first and then see if there are any updates:
To update the mirror list, run:
sudo pacman-mirrors --fasttrack=5
Then check for updates again:
pamac upgrade
Feel free to provide the output(s) here if there are any errors. Also, this can be important, remember to handle any and all .pacnew files. More info:
https://wiki.archlinux.org/title/Pacman/Pacnew_and_Pacsave#.pacnew
I did the above steps and got this as output.
sudo pacman -Syu
:: Synchronizing package databases...
core is up to date
extra is up to date
multilib is up to date
:: Starting full system upgrade...
there is nothing to do
Do kernels not get updated automatically using pamac/pacman? I cannot use pamac right now since I have AUR packages that fail to build 
No, since each major version is its own package.
That might also be because you are out of date. But I don’t think that should influence the upgrade…so please provice the output for:
sudo pacman-mirrors --fasttrack=5
No, as @zbe said, each version is their own package. Installed kernels only get automatic bugfixes, they’re not updated to a newer version.
You could just switch off / disable AUR support, no?
Is it “safe” to change the kernel inside Manjaro’s Settings page? Or is there another approach? I am familiar with Linux in general, I just want to prevent breaking my system accidentally 
From what I’ve heard, it’s safe.
However, I personally use the CLI:
To get a list of available kernels:
sudo mhwd-kernel --list
To install a kernel:
sudo mhwd-kernel --install <kernelToInstall>
Where <kernelToInstall> is the kernel version you obtained from the above command.
To view installed kernels:
mhwd-kernel --listinstalled
To remove a kernel:
sudo mhwd-kernel --remove <kernelToRemove>
Where <kernelToRemove> is the kernel version you obtained from the above command that you wish to remove.
More:
Some more:
Just adding some useful things to the mix:
This command combination selects the (5) fastest mirrors, performs an update using pacman, and performs an update with a forced refresh using pamac:
sudo pacman-mirrors --fasttrack 5 && sudo pacman -Syu && pamac update --force-refresh
It’s usually a good idea to check the mirror status of Manjaro Repositories before attempting an update;
This page explains how to manage kernels:
I hope these are useful. Cheers.
So I went ahead and updated to 6.6 LTS:
$ uname -a
Linux 6.6.26-1-MANJARO #1 SMP PREEMPT_DYNAMIC x86_64 GNU/Linux
The issue still persists. Installing applications through the pamac GUI for example prompts polkit and shows me the dialog, but only the password is accepted. Fingerprint still doesn’t work. I also updated my mirrors after the kernel update, updated all applications on my system (and forced a pamac refresh too).