Bea

The Fast Startup point deserves more emphasis than it usually gets, because the failure is not always loud.

A dirty NTFS volume sometimes mounts read-only rather than refusing. Steam then cannot write, and what you see is games failing to update, saves not persisting, and a library that seems to randomly revert. Nothing says "the disk is read-only" anywhere you would look.

Check how the volume is actually mounted before you debug anything else. If it says read-only, everything downstream is a symptom.

And properly off means the power option, not just avoiding hibernate. "Shut down" with the feature enabled is a hibernate.

This is almost always the storage controller mode, and it is the single most common wall people hit installing Linux on a laptop that shipped with Windows.

Many laptops ship with the NVMe controller in a vendor acceleration or RAID mode rather than standard AHCI/NVMe. Windows works because the vendor driver was loaded at the factory. Linux has no such driver, so from the installer's point of view there is no disk at all — which matches your symptom exactly, including the empty manual partitioning screen.

The fix is to switch the controller to AHCI, but you cannot just flip it, because Windows will then fail to boot for the mirror-image reason: it will be looking for a driver it no longer needs and will not find the disk. Doing it in the wrong order is how people end up reinstalling Windows.

The safe sequence, which works reliably:

1. In Windows, tell it to start in safe mode on the next boot. There is a supported way to do this from the boot configuration; you are telling Windows to load a minimal driver set next time.
2. Reboot into firmware, change the storage mode from the RAID/acceleration option to AHCI.
3. Let Windows boot into safe mode. It detects the changed controller and installs the standard driver.
4. Turn off the safe-mode flag and reboot normally. Windows now boots fine on AHCI.
5. Boot the Linux installer. The disk is there, and the install-alongside option appears with it.

Two other things to clear before you start, both of which can block you independently:

BitLocker. If Windows drive encryption is on, suspend it — or better, decrypt — before repartitioning or changing firmware settings. Changing storage mode alters the platform measurements the encryption keys are sealed to, and you will be asked for a recovery key you may not have written down. Get the recovery key out of your account and save it somewhere physical regardless.

Fast Startup. Turn it off in the Windows power settings. With it on, "shut down" is a hibernate, the Windows partition is left in a dirty state, and any installer that touches it can leave you with a damaged filesystem.

Do those two first, then the storage mode dance, then install.