I've looked at the database schema, but found nothing related. I've looked at the PHP code for the dashboard page at /usr/share/zabbix/dashboard.php, but they use some code I can't quite grasp.
For example:
CFavorite::add('web.favorite.screenids', $id, $favouriteObject)
So, I understand it has to somewhere link that to each user profile. Here are the columns for the profile table, but I can't see where else in the database this information would be kept.
mysql> describe profiles;
+-----------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| profileid | bigint(20) unsigned | NO | PRI | NULL | |
| userid | bigint(20) unsigned | NO | MUL | NULL | |
| idx | varchar(96) | NO | | | |
| idx2 | bigint(20) unsigned | NO | | 0 | |
| value_id | bigint(20) unsigned | NO | | 0 | |
| value_int | int(11) | NO | | 0 | |
| value_str | varchar(255) | NO | | | |
| source | varchar(96) | NO | | | |
| type | int(11) | NO | | 0 | |
+-----------+---------------------+------+-----+---------+-------+
You've identified the correct table. There was partial documentation about this table at https://zabbix.org/wiki/Docs/DB_schema/3.4/profiles , I added more detail just now.
An example of the meaningful fields when a screen favourite entry is stored:
MariaDB [zabbix]> select userid,idx,value_id,source,type from profiles
-> where idx like 'web.favorite.screenids';
+--------+------------------------+----------+----------+------+
| userid | idx | value_id | source | type |
+--------+------------------------+----------+----------+------+
| 45 | web.favorite.screenids | 16 | screenid | 1 |
+--------+------------------------+----------+----------+------+