Here’s my personal recommendations
Grammar - Organic Japanese With Cure Dolly on Youtube
Some people have trouble handling her voice (I’ve never had a problem with it) but she has the most useful explanation of grammar I’ve encountered anywhere.
Onomatopoeia - Onomappu on Youtube
Japanese native that gives explanations on various onomatopoeia from a native perspective. His videos are in Japanese with english subtitles available so it can double as listening practice. Onomatopoeia is used a lot in Japanese so it really helps to understand the concepts behind them.
Conjugation Practice - Katsu 活用
Great for practicing all the conjugations and in which order they combine together
For vocabulary the best method in my opinion is learning it from whatever you’re reading or watching. You’ll remember it better with context.
Otherwise keep an eye on these forums. There’s lots of topics already with lists of extra resources and new ones pop up from time to time. Bookmark whichever one’s you find interesting.