
How I can identify new post on facebook or any other websites.
That's an entire product and service line to monitor web pages, so you would basically be coding your own in PAD.
For that purpose, I general I use Distill.io, which can send emails to alert you on changes that can be used to trigger PAD processes. I have over 1,100 Distill.io's set up, so I sure wouldn't want to code all those in PAD.
But if you don't have many, you can create a monitor yourself in PAD. In short, you would use the Data Extract command to put the web page's posts into a spreadsheet, and then write code to either check for changes to that spreadsheet against the previous run, or check on something else like the date of the post, and run the whole process on a set time interval using a Power Automate "recurrence" Flow.