The addons demo forum will not allow you to login to the dashboard and test the fields. The addons demo only allows test fields on the front-end, but as far as I see there is no such a field on the front. So you may contact gVectors Team and ask them for a demo via supportgvectors.com email address.

I understood you very well. I just mentioned one solution, but it could be in any way. So the answer is still no. There is no way to do this.

but the Topic Prefix cannot turn the tag inserting field to a dropdown or to a select only field.

Thank you for the post and suggestion, and I may look into that addon as well.  I wasn't asking about turning the tag inserting field into a drop down.  Am I misunderstanding how the Topic Prefix addon works?  As admin, you create a set of predefined Prefixes, and then that's what shows up before the topic subject box, correct?  Then when someone posts a new topic, they have to select a prefix?  Can you make that required?

I'm sorry, but the Topic Prefix cannot turn the tag inserting field to a dropdown or to a select only field. The tag field cannot work only in selecting mode, if it's enabled it'll allow inserting new tags or select existing tags.

You could use the "Multi-choice Autocomplete" field type of the wpForo Topic Custom FIelds addon. It allows creating new custom fields in the topic form to let users select multiple predefinded values without allowing them to insert new one. The custom field can be added in the forum search form as well:

https://wpforo.com/wp-content/uploads/2023/12/wpForo-Topic-Custom-Fields-Autocomplete-Field.png

https://wpforo.com/wp-content/uploads/2023/12/wpForo-Topic-Custom-Fields-Autocomplete-Field-Settings.png

If none of the solutions work for you, you can contact to the pro support for custom development: https://wpforo.com/pro-support/#customization

I'm sorry, but there is no way to make tags work that way. If you want a custom feature, you can contact the pro support: https://wpforo.com/pro-support/#customization