If the tool couldn't fix this for you you'll have to do so manually within your database. This happens on older Joomla 3 installs that have migrated over time that never had their database collations fixed. Easiest way to do this is with phpMyAdmin under the Operations tab you can change the collation for all tables and their columns to the correct utf8mb4_unicode_ci.

I would like to automatically fix this for you, but it's too risky for us to be tampering with all your table collations on install of a plugin. Good news is it's a 1 time fix and your database will have the correct collations for the forseable future.

Make sure the _comprofiler_plugin_activity table and its columns all have utf8mb4_unicode_ci collation. You're getting a mixed collation error. For some reason something is set to utf8mb4_general_ci. You need to check the tables you only checked the database itself with the above. Additional fixes have been put in place but they can't fix an existing install.

Ok, have released a new build release that tries to force the table collations. It's not going to fix issues where 1 column has the wrong collation, but should stop this from happening again. You can give this new build a try and see if that works for you.