I used the following site to solve all the possible words for me. Just type each letter(s) into the corresponding box then click solve. After that just look at what the goals are for the stars. https://www.dcode.fr/boggle-solver-4x4
When I got the achievement these were the goals associated with my stars.
1. Typically a score limit.
2. Typically so many of (x) letter words
3. Typically associated with using some letter combination to make a word.