How can I separate accounts from one Quicken subscription into two subscriptions?

What you should have is two separate Quicken data files, one for your personal finances and one for the condo association. you really don't want to have the condo association's finances co-mingled with yours. you can have as many separate Quicken data files as you want, all with your one subscription.

If you used to have two separate data files and you merged them into one by importing them both into the same Quicken data file, that's where things went wrong; each should have been converted separately from the old Quicken to the current one.

In any case, I think you should now look at separating the data into two data files. If the condo association data is pretty minimal, it could be that you just start a ew data file and re-create the data in the new file, and then delete it from your personal file. If there's enough historical data to make that impractical, there's another approach you could follow…

In Quicken with your current co-mingled data, you can select File > Export > Quicken Transfer File (QXF). then do File > New and select Start from Scratch. Let it create a dummy account (select "My bank is not in the list") which you'll soon delete. Then select Import > Quicken Windows File (QDF, QXF), and have it import the file you previously exported. This will be a near duplicate of your existing Quicken data file. In this duplicate, delete the accounts in the left sidebar which are for your personal finances, leaving only the account(s) for the condo association. you will need to re-create any reports you prepare for the condo association, but now your data will be separate. You should use File > Rename to give this file a name which makes clear it's for the condo association. Once you're sure you have all the data for the condo association under control in this new file, go back to your regular data file which still contains both your  personal and the condo association data (use File > Open Recent). Now, you can delete the condo association accounts from this file, leaving only your personal data. This will complete the separation of your one data file into two separate, independent data files with your personal data and the condo association data. Again, you do not need to purchase an additional subscription to do this.

Make an extra backup of your existing data file before you delete anything from it, just in case something goes wrong. But exporting the data, creating a new file, and importing the data into the new file shouldn't impact your existing data file at all. Best of luck!