Normally it’s blocked by default which is pretty easy to get around (It’s just a setting toggle) but apparently Samsung added a second “safety” autoblocker to a recent update. (Which can also be turned off, so I’m not sure what all the fuss is about, aside from being a mild inconvenience.) https://www.androidauthority.com/enable-sideloading-one-ui-6-1-1-3463446/
Ya it’s not a good look of things to come, but so far it’s not a huge issue (yet).