Hey annirooni,
We understand that you're having trouble loading Facebook using Safari on your Mac and your iPad. We definitely want to help! You went through some great troubleshooting steps too. Is this only happening with the Facebook page? Do you have another web browser installed to see if it will open there?
If this is only happening with the Facebook page, when trying to open the page, click and hold the Reload (refresh) button and choose "Reload Without Content Blockers" to see if the page is being blocked by a Content Blocker you may have installed. That step and others can be found in this guide: If you can’t open a website in Safari on Mac
We also recommend completing the steps under "If Safari doesn't load pages from a specific site" here: If Safari doesn't load a page or webpage items are missing
If the issue continues, let's help to further narrow this down by installing available macOS updates, testing in safe mode, and a test user. Here are some great guides to help:
How to update the software on your Mac
Testing in safe mode tells us if a third-party process or application is causing this: How to use safe mode on your Mac
Testing in another user account lets us know if this is a system-wide issue or only happening in your user account: Set up users, guests, and groups on Mac
Keep us posted on the results.
Take care!
