Partition resizing issue on Ubuntu 18.04.6 LTS when booting from usb

Hi all, following this useful article on how to create a partition to install Windows (How to Install Windows After Ubuntu Linux in Dual Boot) but cannot resize the linux partition when booting from a usb. The linux partition should not be mounted but the resize option on the popover is disabled. I also tried doing this on gparted as shown on the attached but the minimum and maximum size appear to be the same.

Has anyone encountered this issue before? Perhaps the partition is active in some other way? Many thanks.

If this partition has been used by timeshift, then it may be locked

Thank you for the response. I’ve not used timeshift. Is there any way to unlock it? What are my options now for trying to resize this partition?

I use a gparted cd to boot my pc and use it to modify and edit both linux and windows partitions.
You could also try the lsblk command to find the mounted partitions.

Have you confirmed this under “Partition - Unmount”?
Bildschirmfoto vom 2022-03-06 22-28-01
Just to be sure.

Ah, @Akito 's Elf-eyes spottet, that it’s LVM…