From your comment it seems like your device is stuck on apple logo where you can’t even use the device itself? If that’s the case, try to do an update on it and see if that resolved the Apple logo issue.
You need to be able to trust the computer 1st to access the device to create a backup, otherwise iCloud is your only other backup option, if you can use the device where you can get to the iCloud menu to manually start the backup.
If you are not able to use the iCloud option due to Apple logo only thing you see, let’s see if we can get past that with updating the device.
Have iTunes opened, ensure you have the latest version of iTunes running. Connect iPhone to computer, ignore the prompts on the computer screen, press cancel and make sure no pop ups are opened.
Press and hold simultaneously the side button (the one you would normally use to power off the device) and the volume down button for about 20 seconds. You should get a prompt in iTunes to update or restore device (or maybe just update and cancel), select update and let it try to update.
If update is successful and you are able to now use the device and access the phone menus and such, you are good now and try to do your backup as you normally would.
If you get an error code that you can’t update or update failed, you may have some hardware/software issues. At that point the only next step to at least try to get the device running normally is to do a restore, but that option will erase you device and you may loose all your data. At this point you may want to stop by an Apple store and see if they can attempt an update themselves.
Good luck M8
