Clozemaster is absolutely phenomenal. I've been using it for Mandarin and (primarily) Greek the last few years. It has sets with the most common words of the language (100, 500, 1000, 2000, 5000 etc) and you get to learn them by filling in the words inside sentences. It doesn't teach you any grammar though, it's only for building up vocabulary.

For Greek, I used language transfer to get the basics and the grammar. It's a great resource, though there aren't that many courses: https://www.languagetransfer.org/free-courses-1