Suggest you log out/in start a fresh session then start again, copy/paste the entire session if error(s) still persist.
I've re-created a session attempting to mimic yours .... the log of that follows ....
OS - linux mint 20.x
mysql - version 8.0.33 ....
mysql -u $USER
mysql> use junkdb;
Database changed
mysql> describe cust;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| stuff | varchar(255) | NO | | NULL | |
+-------+--------------+------+-----+---------+-------+
1 row in set (0.00 sec)
mysql> select * from cust;
Empty set (0.00 sec)
mysql> INSERT INTO cust VALUES ('hi');
Query OK, 1 row affected (0.01 sec)
mysql> SELECT * FROM cust;
+-------+
| stuff |
+-------+
| hi |
+-------+
1 row in set (0.00 sec)
mysql> exit;
Bye