In order to show the result of termfreq() in the solr dashboard as a separate field, you can use the fl= syntax as specified here: https://solr.apache.org/guide/8_3/function-queries.html
You can use the controls available in the SOLR dashboard to generate the URL for you.
First of all you need to add a standard query. Look for the box on the dashboard that has the q above and add something similar to:
Fields to return
Look for the box with fl and add something similar to below:
Note I added a uniqueid to differentiate, but you would most likely change to title field or something.
This might not be strictly be necessary in your situation, but if you are using a broader search query, then you need to ensure the results with higher matches are displayed. In this situation, look for the sort box and add something similar to:
Now when you hit the Execute Query button, it will generate the correct URL with query specified. Yours should look something like this:
Please see screenshot below demonstrating this working as per above.