Probably a lot of different ways to do it, but first we need to confirm that your Accountant has other versions of QBs besides the QBDT2021 you mentioned. Most Accountants I know have multiple versions for clients that have different versions. If she has QB2020, you might log into your Intuit account and see if you can download the Windows version for the 2020 license you have. If you can, you're all set.
If she does not have 2020 or you cannot download the Windows version, then your best option is probably to buy QB2021 and then keep in sync with whatever version your Accountant is using going forward.
On the Accountant Copy, yes, you can continue to work. You cannot go back in time prior to the Accountant's Copy and make changes, but you can look things up. When your Accountant gets done make her changes, they will change only the things prior to the time/date you made the Acct Copy. Any work you've done after that will stay the same. Not on the Mac, it does not have Accountant Copy, so if you send a Backup, you need to wait until she send you back the corrected file or sends you a list of entries to make those adjustments.
That's why my process is to set up a time with the Accountant. Used to go to the office, now it's a Zoom or sometimes a Desktop Share. Either way, we look at the file and make the changes needed. In the early days the old Accountant had done things that didn't make sense to me or to my (then) new Accountant. So they'd give me some marching orders and I'd go make changes as I had time. Then we'd get together and review. Now the changes are more things on the edge like are we depreciating X or is it small enough to just list as an Expense. Little things like that.
