Yep - you can generally proceed with the Windows 10 USB repair tools. X: is typically the temporary RAM drive used by the Windows Recovery Environment, and it is not normally your actual Windows installation or your personal-data drive.
Do not back up files from X: just because they are there. Those files are part of the recovery environment and will disappear when you reboot.
Before doing any repair operation that could modify the Windows installation, however, make sure your important personal files are backed up from the actual Windows drive (usually C:, but it can have a different letter when booted into WinRE). If you are uncertain which drive contains your Users folder and personal files, check that first.
If your USB was created with Microsoft's Media Creation Tool, you can boot from it and select Repair your computer rather than Install Windows. That gives you access to Startup Repair, System Restore, Command Prompt, and other recovery options without immediately reinstalling Windows.
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hth
Marcin