My favorite dictionaries available in Pleco as someone who knows Mainland Mandarin are the following:
现代汉语规范词典 - great for learners as it focuses on very standardized mainland Mandarin
Both French Ricci dictionaries - they contain info on characters similar to Outlier and a lot that Outlier doesn’t currently have, so it’s a great companion
Outlier - I have the expert one, great if you want to know about characters’ original meanings and designs.
汉语大词典 - basically if it’s ever been a word, even historically, it’ll show up here. This dictionary has saved me a bunch when reading formal texts. It’s great if you love literature and expect to see lots of rare, formal, or archaic words
Student’s dictionary of Classical and Medieval Chinese - if you want to read classical texts, this is your dictionary
多功能成语词典 - the best Chengyu dictionary with 8000 entries. I rarely come across idioms not in here
ABC proverb dictionary - this one is good for 谚语 and 俗语, idioms that won’t be covered by 成语 dictionaries