Havent you experience such or you have a fren having same issue?
Hey there! Season's Greetings!
First off, apologies for any inconvenience brought about by such. As per Samsung Korea, this issue is caused by the increased physical attributes of the S20 Ultra's 108MP camera sensor.
The focal length is determined by the lens specifications
According to the Samsung moderator, the increased size of the S20 Ultra’s sensor results in a shallow depth of field and a longer focal length of 10cm or more, therefore, it may fail to focus when photographing objects up-close. More importantly, because the focal length is determined by the lens specifications, this shortcoming is difficult to correct with software.
In other words, autofocus should no longer be an issue for the Galaxy S20 Ultra in general applications, but a loss of focus can still occur at close range due to the focal length being longer than usual (the Galaxy S20 and S20+ have a slightly shorter focal length as they use a different main camera sensor). Basically, it’s a physical characteristic of the Galaxy S20 Ultra’s 108MP camera that owners of the device will have to live with.
Still, here's a quick remedy on how you may achieve that desired shot.
"Zoom the camera to 1.5x before telling the user to ‘move a bit farther away.
Changing the camera distance like this does cause a small change in perspective, but doing so allows the camera to capture a close-up image that’s as similar as possible to what the photographer intended."
Check out the links below with regards to the whole article on said issue and with regards to the quick fix.
Hope to have helped as well! Thank you for your unwavering support for Samsung. Keep safe and have a wonderful week ahead. God Bless.😊