The problem with using First Touch is that Facebook may not be your first touch...
Facebook works by adding a user being on FB and clicking on a ad... this drops a cookie onto the user's computer (for all we know, users may cancel the page load before the site loads and records our own analytics).
If in the next 30 days (at least by the default setting), that user "converts", because FB sees that cookie on their machine, they will treat that as their conversion... not terribly realistic.
Then you also need to take into consideration your own internal traffic (which should be excluded), Bot / Spammer traffic that you should have excluded, the fact that FB is uing a different way of tracking which may not fit the same "opt out" structure, or same client level "blocking" which we all know we lose data to, etc.
Trying to mix what FB is saying with what Adobe is saying is "comparing apples and oranges".
Given how "greedy" FB is, and considering that users may cancel out of the click before they actually arrive on the site, most people will just defer to Adobe's tracking...but that is a decision that you and your business need to decide on.
Being armed with some understanding of what FB is doing will help you to understand and make that decision for yourself.
There have been other posts this year alone, all asking similar things:
https://experienceleaguecommunities.adobe.com/t5/adobe-analytics-questions/discrepancies-between-adobe-analytics-and-facebook/m-p/544790
https://experienceleaguecommunities.adobe.com/t5/adobe-analytics-questions/data-discrepancies-between-facebook-ad-adobe-analytics-reports/m-p/247782
This is pretty much a universal problem...