From the documentation (MySQL 8) :
Type | Maximum length -----------+------------------------------------- TINYTEXT | 255 (2 8−1) bytes TEXT | 65,535 (216−1) bytes = 64 KiB MEDIUMTEXT | 16,777,215 (224−1) bytes = 16 MiB LONGTEXT | 4,294,967,295 (232−1) bytes = 4 GiB
Note that the number of characters that can be stored in your column will depend on the character encoding.