Synchronization with publicly sharable app

All -

One of the biggest downsides of To Do is the fact that you can't share it with people external to your organization. I thought I'd be smart and just create a synchronized enviornment with any publicly available app. That could be planner, but also Asana, Monday.com, etc.

Has anybody accomplished that? Or perhaps even better: is there a downloadable tool, template, explanation and/or code to implement this?

I have tried several tools to synch it with Asana, but they either work only one-way (Pleexy) or are cumbersome/expensive to set up (Zapier). 

I am pretty sure that you can set it up with Power Automate, but I think it would similarly be cumbersome.

Joy