How can I import my Mint data? Will my categorizations upload if I do?

You can use my software for this which is called ImportQIF and is free. The best output format is QIF (which is the default for ImportQIF) because it allows for categories and tags, whereas the QFX format doesn't. What's more QIF can be imported into an account that is already setup for online download whereas for QFX you would probably have to turn that off first.

The categories will be created on the fly while importing. Note that you might have to go back and change categories to income (or expense) if they are set wrong. I suspect that Quicken will mostly guess that the new categories are expense. Also, because the account types will be created on the fly and maybe not what you want and Quicken has very few options to changed them after the fact, you might want to pre-create the accounts. The account names can come from account column. Another possibility is to either do each account separately and not use the account column, and that way the name will come from the one given to the account in the Setup tab and have the account type selected there. Or could use the account column and do all of the same account types together. Note that the QIF import limits the account names to 40 characters.

As for investment accounts, I didn't keep up with if Mint supports investment transactions. Way back when, it didn't, only balances. If it does (did), I would import them one account at a time, and definitely create account first. Also, QIF imports securities by symbol, so you should create all securities first and make sure they have symbols. Importing investment transactions is a lot harder than non-investment transactions because not only do you have to map the columns to the correct field in the QIF File/Quicken, while doing the conversion you have to tell ImportQIF what each security action is, since there isn't any standard on the names. Like Buy, Bought, …

As for duplicates. You will certainly have duplicates for every transaction that overlap with transactions that you have downloaded with Quicken's connection types. The QIF import puts the transactions in the register without any processing.

I suggest that you reconcile all the transactions in the register before doing the import(s). That way at least you can tell which transactions were just imported. And make a copy of your data file (Windows File Explorer copy is fine) before starting so that you can go back just in case something goes wrong. And for various reasons I recommend a "Windows File Explorer copy" over Quicken's backup.

You can find ImportQIF at my website: https://www.quicknperlwiz.com/

This is excellent! I have 9700+ transactions in Mint since I started using it in 2011. The funny thing is I used Quicken Basic in the late 90's. I should never have left. I remember my wife hand entering our checkbook information when we first started using Quicken back then. I did not want to relive that moment since we have to migrate from Mint.