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 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.