I have had Win 10 on my PC for years with many updates, now Ver. 1709 16299.98 (yes this is an odd number isn't it?) and went to 'Backup and Restore (Windows 7)' yes Windows 7 - why is that?
Because it's the backup utility that's been around since Windows 7 and was carried over, intact, to Windows 8, 8.1, & 10.
It's also been deprecated and Microsoft suggests using a third-party backup tool at this point in time. My favorite for ease of use is EaseUS To Do Backup.
After 2.5 hours, and not yet finished, going to Details it says Windows backup ...100% complete but under this it says, Windows backup is currently in progress.
No surprise here, either. It typically takes hours to do a full system backup on any machine that's not in "out of the box" fresh state and that has any significant amount of user data on it. A full backup for my machine which has just under 500 GB of used space on the hard drive typically takes three hours or more. Incremental backups take less time, but still generally between 1.5 and 2 hours (since I don't do these until I feel the system has had enough changes since the last backup that I wouldn't want to have to do over again).
If you want to make a backup I really do suggest you look into third party options like EaseUS To Do Backup, AOMEI Backupper, Macrium Reflect, or similar. While I generally like using built-in Windows utilities given that Windows Backup is (and has been, for some time) significantly slower than third-party options and uses far more space for its backups I have abandoned it. There's also the fact that Microsoft is pretty much telling you that it will eventually disappear and to use the time it has left to find an alternative.
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall