"Authentication failed" with Pamac

When I try to update something in pamac, I get “Authentication failed”
Output:

Preparing…
Cloning franz build files…
Checking franz dependencies…
Cloning electron9-bin build files…
Checking electron9-bin dependencies…
Authentication failed

There is no “enter password” dialogue. Only an “Authentication failed” dialogue.
I changed my password today and did some changes in PAM.

How can I fix this?

Like what?

I followed this guide yesterday and did most of the things to harden my setup:
https://theprivacyguide1.github.io/linux_hardening_guide

This is my /etc/pam.d/passwd:

#%PAM-1.0
#password required pam_cracklib.so difok=2 minlen=8 dcredit=2 ocredit=2 retry=3
#password required pam_unix.so sha512 shadow use_authtok
password required pam_unix.so use_authtok sha512 shadow rounds=65536 retry=15 minlen=10 dcredit=-1 ucredit=-1 ocredit=-1 lcredit=-1

password optional pam_gnome_keyring.so

I also read that this issue could be related to polkit. I reinstalled polkit and pamac and rebooted. I also checked if polkit was running with:

$ sudo systemctl status polkit

output:

● polkit.service - Authorization Manager
Loaded: loaded (/usr/lib/systemd/system/polkit.service; static)
Active: active (running) since Mon 2020-11-16 08:52:49 CET; 23min ago
Docs: man:polkit(8)
Main PID: 839 (polkitd)
Tasks: 8 (limit: 9384)
Memory: 21.1M
CGroup: /system.slice/polkit.service
└─839 /usr/lib/polkit-1/polkitd --no-debug

Polkit seems to be fine.

I managed to fix it.

The problem is in /etc/fstab:

proc /proc proc nosuid,nodev,noexec,hidepid=2,gid=proc 0 0

I turned it off with:

#proc /proc proc nosuid,nodev,noexec,hidepid=2,gid=proc 0 0

it is possibly also fixable by adding my user to the proc group.
and probably also by disabling firejail (sandbox)
but I chose to disable the above line in fstab to fix the problem.