Are you using a MVNO or do you have service coming directly from a carrier?

Why I flash. Too many OTA upgrades without a fresh start.

Every time I haven’t, I’ve regretted it.

You could wipe it clean using the bootloader and do a factory reset.

https://android.gadgethacks.com/how-to/boot-your-galaxy-s10-into-recovery-mode-download-mode-0194521/

I only buy older phones. Current phone is a Note 10 plus with a minorly cracked screen.

I always reflash the system using Odin when I get a “new” phone. Smooths things out.

https://android.gadgethacks.com/how-to/use-odin-flash-samsung-galaxy-stock-firmware-0182037/

I could be wrong, but I was just looking at this the other day and it looks like there is a backup option to an SD card, so that may mean an external OTG memory device could also be used.

Smartswitch makes life easy.