how to enalbe MySQL 8 innodb_dedicated_server option
(I wrote a bug report about that doc page.)

You do not have any other apps (Apache, Java, etc) running on the machine, correct?

Plan A:  Manually with innodb_buffer_pool_size = 1200M, I think 2G is too big for 4G of RAM.

Plan B:  Write a bug report.  In it provide your entire my.cnf and the exact version you are using (bugs.mysql.com).  Then abandon innodb_dedicated_server = ON.