Most repairs never touch your data, but a device that is already failing can stop working at any time. A backup before the repair takes ten minutes (sample note).
Turn on the phone’s own cloud backup or copy it to a computer. Write down which apps hold your two-factor codes and move them to the new backup too: they are the part people forget.
On a laptop, copy your documents, desktop and photo folders to an external drive. If the laptop will not start, bring it in as it is: data recovery is a separate service.