https://www.japandict.com/ - an online dictionary of words, idioms, kanji, and radicals
https://tangorin.com/ - here you can not only look up words but also example sentences with them
https://www.youtube.com/channel/UCBSyd8tXJoEJKIXfrwkPdbA/videos - a channel with lessons about Japanese grammar, vocabulary, culture, useful phrases, and more!
https://www.ganganonline.com/ - here you can read manga in Japanese for free
http://www.guidetojapanese.org/learn/ - this website has some assimilable and helpful articles on Japanese grammar
https://jlptstudy.net/ - study materials for JLPT
Feel free to share your own discoveries regarding helpful online sources for learning Japanese!
The first one is the AJATT table of contents, which provides all the resources and methodology to follow in order to learn Japanese.
The second one is NukeMarines guide to Japanese Literacy, which can be combined with the AJATT method.
If you have any questions about my own personal plan on studying Japanese you can email me, I think both of these sources are very good to follow.