sudo apt install pcscd pcsc-tools opensc
Get driver from https://abcircle.com/en/product/2/CIR115B/sim-sized-contact-smart-card-reader/ (at the time of writing version was 2.2.1)
sudo dpkg -i libabcccid_2.2.1-1_amd64.deb
Snap package is not working for some reason (details misho-knowledge-base/stampit#3), so remove snap package and use an official mozilla PPA to install firefox: https://fostips.com/ubuntu-21-10-two-firefox-remove-snap/
Reboot the PC after installing the PPA package. OpenSC provided stampit-authenticator should show up in Settings -> Privacy+Security -> Security Devices.
Extract https://github.com/misho-knowledge-base/stampit/blob/main/resources/CSSI_Client_5.0_Linux.zip . Go "Settings -> Privacy+Security -> Security Devices -> Load" and load the .so.
Install Okular
sudo apt install okular
Tools -> Digitally Sign. This should automatically work. If not please follow (http://wiki.infonotary.com/index.php?title=Instructions_for_signing_documents_with_qualified_electronic_signature_in_Okular )
sudo apt-get install libnss3-tools
mkdir -p $HOME/.pki/nssdb
modutil -add "OpenSC" -libfile onepin-opensc-pkcs11.so -dbdir sql:$HOME/.pki/nssdb -mechanisms FRIENDLY