Updates are sent out in connection to region, phone model, build and serial number and some networks ask Samsung to hold off sending out updates to their branded phone's i.e phone's supplied by them while they test out the update.
Sammobile.com has some information on the update for that phone model > https://www.sammobile.com/news/galaxy-a71-android-12-update-released.
You could check using Samsung Smartswitch or you could look at manually updating the software yourself by looking at the options on the xdadevelopers website.
Disclaimer >
If a person manually updates their phone's software and it goes wrong causing potentially stability issues and functions and features not working then Samsung may then charge a fee to put this right.
It's essential that a person learns on how to do this type of update properly and uses the correct software for their phone and region.
My advice is to wait for the official update via Samsung Smartswitch or via the phone's software update section.
I wish you all the best. 
