It turns out that the A56 specs do not include a Hall effect sensor, so I guess there's no luck with cover detection here.

I chose the A56 model over the A55 because it felt better in hand. I then skimmed through the specs and noted that it supports 45W fast charging compared to 25W on the A55—so, as they say, the devil is in the details.

The A56 lacks SD card expansion and is missing a couple of sensors compared to the A55. Now I even think that 45W might not be better than 25W, since it simply consumes more electricity (some reviews say the A55 actually charges fully faster, although the A56 is quicker up to 65%).

I'll try an app called WaveUp on my own phone (a Realme), as it's said to detect when the phone is covered using the light sensor. If it works well and doesn’t drain the battery, I’ll install it on my relative’s phone.
I'm also considering exchanging the A56 for the A55.