I've had a nightmare (ok not an end of the world nightmare) reinstalling with my only ever Google account on two fresh phones on two occasions in two weeks. Google backup doesn't work at all in my experiences or I'm even dumber than everyone thinks. I'm also 90% sure I've lost 9 months of Google Photos as they were also missing via Chrome on Windows last week.
So do other backups as well. I had 2 Samsung phones 2012 - 2015 and they had a decent system then, but having a pc I think helps.
That A20S came out a year ago, which is why I thought you meant the A21s, but it's decent enough.
According to sites if its not on Android 10 now you will fired a big update over the air, as well as Samsung's latest UI, 2.5 or something. I hope you have enough data or WiFi somewhere.
You'll probably get several separate monthly security patches, best to get them over with.
My experience is not to fill up with all your favourite apps as installing the updates takes much longer when it has to update all the apps each time.
I did notice a hole on top was mentioned assuming you knew it would be next to the sim and card tray so unfortunate but I hope you haven't inadvertently damaged the hole for the secondary ambient microphone for assessing noise during calls, or something like that. It's probably OK unless you grabbed a hammer in frustration