Why table charset uses utf8 not utf8mb4

Hi,
I store some text in process variables, including emoji, but the table created by camunda uses utf8.
I would like to ask why camunda chooses to use utf8, and then can I change the table to utf8mb4?

I use MySql:
https://github.com/camunda/camunda-bpm-platform/blob/master/engine/src/main/resources/org/camunda/bpm/engine/db/create/activiti.mysql.create.engine.sql