@RadioMick Thanks

on my Redmi Note 9 pro i get this

phablet@ubuntu-phablet:~$ df /
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/system 3026216 3000464 0 100% /
phablet@ubuntu-phablet:~$

Although I didnt install too many packages.
How to fix this ?

Thanks