Like this (LVM based)

root@srv65:~# lvs | grep 1071
  vm-1071-disk-0 BigStore -wi-a-----  64.00g                                                    
  
root@srv65:~# e2fsck -fy /dev/mapper/BigStore-vm--1071--disk--0 
e2fsck 1.46.5 (30-Dec-2021)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/mapper/BigStore-vm--1071--disk--0: 35234/4194304 files (0.1% non-contiguous), 628897/16777216 blocks

root@srv65:~# resize2fs /dev/mapper/BigStore-vm--1071--disk--0 8G
resize2fs 1.46.5 (30-Dec-2021)
Resizing the filesystem on /dev/mapper/BigStore-vm--1071--disk--0 to 2097152 (4k) blocks.
The filesystem on /dev/mapper/BigStore-vm--1071--disk--0 is now 2097152 (4k) blocks long.

root@srv65:~# lvreduce -L 9G /dev/mapper/BigStore-vm--1071--disk--0
  WARNING: Reducing active logical volume to 9.00 GiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce BigStore/vm-1071-disk-0? [y/n]: y  
  Size of logical volume BigStore/vm-1071-disk-0 changed from 64.00 GiB (16384 extents) to 9.00 GiB (2304 extents).
  Logical volume BigStore/vm-1071-disk-0 successfully resized.

root@srv65:~# resize2fs  /dev/mapper/BigStore-vm--1071--disk--0
resize2fs 1.46.5 (30-Dec-2021)
Resizing the filesystem on /dev/mapper/BigStore-vm--1071--disk--0 to 2359296 (4k) blocks.
The filesystem on /dev/mapper/BigStore-vm--1071--disk--0 is now 2359296 (4k) blocks long.

root@srv65:~# vim /etc/pve/lxc/1071.conf