Debian 11 : libappindicator3-1 unmet dependency makes riseup-vpn package installation FAIL

Hi there, new to 0axacab, thanks all the team for riseup-vpn. It used to work very good on Debian 10 BUT on Debian 11 bullseye the package installation (as described in https://riseup.net/en/vpn/linux#package-installation) fails :

steps to reproduce : 1 - sudo apt install leap-archive-keyring OK 2 - echo "deb https://deb.leap.se/client release buster" | sudo tee -a /etc/apt/sources.list.d/leap.list OK 3 - sudo apt update OK 4 - sudo apt install riseup-vpn FAILS : (I traduce from french error message:) following package have unmet dependencies: riseup-vpn : depends : libappindicator3-1 but can't be installed

Thank you if you have any advice or answer to this issue.

Debian 11 Linux TP 5.10.0-8-amd64 #1 (closed) SMP Debian 5.10.46-4 (2021-08-03) x86_64 GNU/Linux