I try the following statements on MariaDB-10.8.2:

DROP TABLE IF EXISTS t0;

CREATE TABLE t0 (c0 varchar(5));

INSERT INTO t0 VALUES('a'), ('1');

DELETE FROM t0 WHERE NOT c0;

The DELETE statement deleted the first row, and a warning was generated.
I try a UPDATE statement, which share the same where clause with the above DELETE statement, as follows:

DROP TABLE IF EXISTS t0;

CREATE TABLE t0 (c0 varchar(5));

INSERT INTO t0 VALUES('a'), ('1');

UPDATE t0 SET c0 = 'b' WHERE NOT c0;

The UPDATE statement failed and generated an error.
I think the data truncation of value 'a' should also cause this DELETE statement errors instead of a warning. Because UPDATE and DELETE are both data-change statements.