If you don’t do lvm and can’t reinstall the system, you can’t expand the root partition.
However, you can expand the directories that need additional space. If you only need to expand a few directories, you can do this:
1) Add a new hard disk partition and format it
2) Mount it on an unused directory, and then Move the contents of the directory that needs to be expanded to this directory (you need to stop the programs that are still using the files inside)
3) Unmount the new partition and remount it to the directory that needs to be expanded
Repeat the operation for multiple directories