Unable to LOAD_FILE in Maria DB

I am using Maria DB on Ubuntu 1804 :

Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 37 Server version: 10.1.44-MariaDB-0ubuntu0.18.04.1 Ubuntu 18.04

I want to do something relatively easy and I have wasted 2 hours on it. I want to load a file as a string. There are several questions (many of them really old) on this site but none of them lead me to a solution and I have tested everything til reaching total frustration.

Granting privileges :

MariaDB [(none)]>  GRANT FILE ON *.* TO matias@localhost;;
Query OK, 0 rows affected (0.00 sec)

ERROR: No query specified

MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> SHOW GRANTS FOR matias@localhost
    -> ;
+-----------------------------------------------------------------------------------+
| Grants for matias@localhost                                                       |
+-----------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'matias'@'localhost' IDENTIFIED BY PASSWORD '*???' |
+-----------------------------------------------------------------------------------+
1 row in set (0.00 sec)

No secure_file_priv :

MariaDB [(none)]> SHOW VARIABLES LIKE 'secure_file_priv';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| secure_file_priv |       |
+------------------+-------+
1 row in set (0.00 sec)

Right permissions on the file :

[~]@Ubuntu1804  #> ls -lh test.txt
-rw-rw-r-- 1 matias matias 6 Feb 29 23:44 test.txt

And still cant get the file :

MariaDB [(none)]> SELECT USER();
+------------------+
| USER()           |
+------------------+
| matias@localhost |
+------------------+
1 row in set (0.00 sec)

MariaDB [(none)]> SELECT LOAD_FILE('/home/matias/test.txt');
+------------------------------------+
| LOAD_FILE('/home/matias/test.txt') |
+------------------------------------+
| NULL                               |
+------------------------------------+
1 row in set (0.00 sec)

Can someone point me on the right direction to solve this?

Note : I asked exactly this in StackOverflow here : https://stackoverflow.com/questions/60470783/unable-to-load-file-in-maria-db