Short answer: yes. Mattermost v11 will remove all support for MySQL. Might as well get it over with sooner than later!
For your old instance, you probably need to upgrade to 5.37, which is the first ESR release after 5.32. Then 6.3, 7.1, 7.8, 8.1… See Release Lifecycle - Mattermost documentation
Note that in 9.4, support for MySQL 5.7 was dropped in favor of 8 Mattermost changelog - Mattermost documentation
My best guess is you need to get Mattermost upgraded to about 8.1 and then migrate to Postgres. But read though those docs! 