Looks like you didn't install GPlay Services, so Molly will use Websocket for push notifications if unable to detect and use Google FCM. The same is true if you installed The Molly-FOSS version. I have no experience with the Molly UnifiedPush version.
So, Signal/Molly is known for higher battery usage when using websocket connections.
By the way, here (#8880) I'm talking similarly about overnight drain since GOS firmware migrated to A14. I'm with 6a, the OP with 7a.
For me, it is not an app-specific but rather a connectivity problem. If I spend the night in airplane mode or with WiFi and mobile data off - then only 2-3% overnight battery usage as it was with A13-based GOS firmware even with WiFi on.