So for those out there that are having a tough time with the expert puzzles. You can use this site to help you find those GEM catching words. Since you aren't timed on the puzzles just enter the puzzle letters into the grid on that site and hit submit and it will give you every possible pattern. My advise for expert is look through all of them for the words that hit the most gems in a single word. You will end up with more rainbow gems that give you bonus points, which will help make it easier to reach the required score for the puzzle.
Credit to CandidFever3 who posted a new puzzle solver in the comments (thank you):
https://www.dcode.fr/For puzzles with no double letter squares this one is best: (Some in comments have said has issues as an FYI, but page still loads for me but I've not tried actually using it lately.)
https://words-solver.com/wordament-cheat/For the above URL, when you enter the letters into the puzzle and hit submit, it will blank out the puzzle but scroll down and you will see all the possible word solutions mapped out. This works perfect for finding the word that will hit all the crystals you need to collect.
For puzzles with multiple letters in a square use this one:
https://www.dcode.fr/wordament-solverHope this helps.