I had the same problem last week and solved it by doing :
$ df -kh /
Sys. de fichiers Taille Utilisé Dispo Uti% Monté sur
/dev/disk/by-uuid/xxxx 3,6G 3,4G 79M 98% /$ sudo resize2fs /dev/mapper/crypt_root
resize2fs 1.46.2 (28-Feb-2021)
Filesystem at /dev/mapper/crypt_root is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 4
The filesystem on /dev/mapper/crypt_root is now 7509504 (4k) blocks long.$ df -kh /
Sys. de fichiers Taille Utilisé Dispo Uti% Monté sur
/dev/disk/by-uuid/xxx 29G 3,4G 24G 13% /
$
Hope it helps