I’m not aware of any great FOSS/FLOSS Tasker alternatives. There are a few options, but they will be less capable, functional, extensible, user friendly, or modern.

More direct alternatives

• Automation - Gitea repo / F-Droid
• Easer - Github repo / F-Droid

Requires a server to run automations/dcripts

• Home Assistant - Github repo / F-Droid

Requires scripts and may require a server and/or additional add-on apps

• Termux - Github repo / F-Droid
  • Termux:API - Github repo / F-Droid

I believe you’re looking for Easer, though not sure how well it matches to your criteria https://github.com/renyuneyun/Easer https://www.f-droid.org/en/packages/ryey.easer/

I also was searching for an open source alternative. I came across Automate, and fell in love with it. However, it’s not open source but I highly recommend giving it a try.