Hey there Kevin
The S21 will be coming out of support in the not too distant future so would recommend going for S22 Series or newer.
S Series do not have SD Card Slot so ensure you purchase a device with enough memory. S22 Series starts with 128gn (some of which is used for System), then 256gb and I think 512gb. Obviously the more the memory, the higher the cost of the device.
Would also recommend backing your device up (for example to Google One, OneDrive or similar (there will be costs for this).
S24 Ultra