Generally, it's perfectly safe to do a factory reset as long as you immediately restore your most recent iTunes backup. iTunes will do this automatically for you when you select "Restore".

If your iTunes backup is encrypted then your phone will be restored to almost exactly as it was (you have to set up Apple Pay again, but everything else is good).

As an iOS developer who tests on many iOS devices, I'm required to do that kind of iTunes backup/restore a lot more often than normal, across different kinds of iOS devices. I find that iTunes backup/restore is very reliable and I highly recommend regularly using iTunes to backup your devices.

When I switch devices or get a new device, it's iTunes backup/restore all the way. (I'm a lot less confident in iCloud device backups, and I don't use iCloud device backups myself.)

If you suspect there's a problem with your iPhone, such as apps that are misbehaving or losing data, the iTunes backup/restore is the first and best option.

If there's still a problem, make a backup and then do a factory reset without restoring the backup (you can always restore the backup later). If it's still a problem, you have a hardware issue.