I have a BTRFS filesystem for Linux, but dual-boot Windows 10. Windows refuses to complete updates due to there being "insufficient disk space". There was around 20 GB free but apparently that still isn't enough.
My solution was to remove the BTRFS partition from the disk that contains the Windows partition so that the partition can be easily extended. This freed up around 90 GB on the disk. Once done, the Windows partition was extended to include the 90 GB.
On booting into Windows the disk size... is the same. Still only 20 GB free.
One suggestion is to shrink the partition and extend it again. I shrank the partition but only by 17 GB because that's all Windows offered.
I extended the partition again but it makes no difference.
chkdsk reports no issues. I ran an "optimise" (discard) but it made no difference.
I have 90 GB missing and no idea how to solve it.