This has been reflected in older pre-5.4 doc for count() function:

like (default) ... are supported for string, text and log items

https://www.zabbix.com/documentation/5.2/en/manual/appendix/triggers/functions

But because of trigger functions refactoring:
https://www.zabbix.com/documentation/5.4/en/manual/introduction/whatsnew540#function-changes
the "(default)" particular details has been lost in a newer doc page for text items:
https://www.zabbix.com/documentation/6.0/en/manual/appendix/functions/history?hl=default

Currently it looks like "eq" is default for any information type - string or numeric, which is not true!

Actually "like" is used by default for count(), countunique() and find() functions for text items.
I've tested count() and find() on v 6.0.17 to be sure, see attachments.
I believe countunique() behaves the same way as count() in this regard.
I had 4 triggers and send values to an item in these triggers, trigger name ends by ({ITEM.VALUE}), so generated problems reflect a value received. See attachments.

So, 6.0+ doc should be updated and the lost detail should be added.
Maybe not supported versions doc (5.4, 6.2) also could be fixed, up to you.