Hello,
Unfortunately Blokada on iOS cannot work simultaneously as another VPN is active as the other VPN will override the settings.
Please consider Blokada Plus for having a VPN together with the ad-blocking feature.
Another option is to use Blokada Cloud together with the iCloud private relay, which is not a real VPN but increases your privacy in Safari and could be considered somewhere in between Blokada Cloud and Blokada Plus.