WordPress does not support MySQL 4 :

To run WordPress your host just needs a couple of things:

 

MySQL version 5.0 or greater (recommended: MySQL 5.5 or greater)

 

https://wordpress.org/about/requirements/

While the utf8mb4 encoding is recent change and you might work around it, overall you still need compatible MySQL version.

WordPress does not support MySQL 4 :

To run WordPress your host just needs a couple of things:

MySQL version 5.0 or greater (recommended: MySQL 5.5 or greater)

https://wordpress.org/about/requirements/

While the utf8mb4 encoding is recent change and you might work around it, overall you still need compatible MySQL version.