just posting an update in here for others that want to try that setup, i think someone in my community might’ve found how to get it to work:
Just need to follow http://www.dds6qkxpwdeubwucdiaord2xgbbeyds25rbsgr73tbfpqpt4a6vjwsyd.onion/wiki/Whonix-Workstation_Firewall#Additional_User_Custom_Firewall_Rules, adding the following rules to the /usr/bin/user-firewall-script file:
#!/bin/bash
set -euo pipefail
# Allow Docker to access the Internet via Tor
nft insert rule inet filter forward index 0 oifname docker0 counter accept
nft insert rule inet filter forward index 0 iifname docker0 counter accept
apparently this works as intended, but i didnt test it myself yet