I would suggest do not waste time waiting and get started asap. Start with a mock test to get a score and see which topics you need to improve.
MGMAT's All the gmat set is good, using it myself (mainly for their online platform + 6 CATs). It's not great for 650-680+ scores but it goes over the fundamentals pretty well. I have downloaded their supplement ebooks but haven't gone through them yet. Honestly, I don't think there is much difference between the OG 20 and OG 21. You will easily find docs and posts on here, mapping questions of OG 20 to OG 21. You will also get enough practice if you buy the set of 3 - OG and the 2 reviews plus you will get
MGMAT's question bank as well. When you say manhattan maps OG 20, if you mean the navigator feature, then know this that when they upgrade to OG 21, you can still access the OG 20 version. I am able to see all the versions till OG 12. Also since the two versions aren't very different, it won't be very hard for you to follow through with the updated version.
If you're asking for other course recommendations, then I'd say the Veritas books are not bad either. Over the past couple of weeks, I left
Mgmat and started using veritas. I got their textbooks and downloaded their free android app (access to all their lesson videos from the on-demand course). My process is - go over each textbook first, then watch the respective lesson videos and then solve the homework questions (around 80-90 each book) for practice. Another recommendation would be TTP, haven't used it personally but it's pretty much the best for Quant. It can get a bit too intensive and long (they say 180 hours for the whole quant), but if you need help in mainly quant then go for this. I would suggest before deciding on any online prep course, take their trial option and try them out to compare and get a feel of the platform, and pick the one that suits you the best. If you need any other help, feel free to ask

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