The monthly Windows updates use several gigabytes of storage space on your hard disk. Most of that's freed up once the updates complete, though you can free up more running Disk Cleanup &/or this command with the Command Prompt [I run both]: dism /online /Cleanup-Image /StartComponentCleanup . You can also empty the 2 temp folders, clear browser caches, delete the C:\Windows\SoftwareDistribution\Download folder, and delete/clear any restore points -- those steps plus disk cleanup & the DISM command can get you close to where you were before the update(s) when it comes to disk space used.
Now, if you don't have that several gigabytes of free disk space Windows updates need & use, that's a problem. Windows updates may look for space on an attached drive/partition, or it may ask you to plug in a USB stick or drive -- I say *may*, because in my experience it's been inconsistent. And it's been enough of a problem that Windows now reserves around 7GB for it's own use installing updates etc. It doesn't actually set aside that storage -- the image backup app Macrium Reflect for example does not include that reserved disk space in its disk display or backups -- but it does deduct it from the free disk space shown in a partition's properties in File Explorer, and it prevents you from using that disk space. The maximum reserved seems to be ~7GB -- from what I've read it could be less, depending on stuff like the optional Windows features installed.
When Reserved Storage was introduced it was only enabled in fresh Win10 installs, & may or may not be enabled in Win11, e.g. it's enabled in a Win11 VM but not for the Insider copy or build on this PC. The easiest way to manage it is using the Command Prompt or PowerShell -- right click the Start Button & in Win10 you'll see Command Prompt or PowerShell in the context menu... use whichever is listed in that menu. In Win11 that context menu shows the Terminal app, which works just as well -- it will open using PowerShell or the Command Prompt, and either one will work. The 3 commands you use for checking if Reserved Storage is enabled, and to turn it on/off are:
For the Command Prompt
DISM /Online /Get-ReservedStorageState
DISM /Online /Set-ReservedStorageState /State:Disabled
DISM /Online /Set-ReservedStorageState /State:Enabled
For PowerShell
Get-WindowsReservedStorageState
Set-WindowsReservedStorageState -State Disabled
Set-WindowsReservedStorageState -State Enabled