Hello Garrett. BLS-2021 (and the soon to be released BLS-2022) do not support Mystery Doubles.
You can reduce the manual/dual entry by importing data directly from BLS-2021 into TBrac-2018.
Chapter 12 of the TBrac-2018 manual has a detailed description of the steps, but here's a quick overview:
1. Have a unzipped copy of the BLS League on the same machine
2. Open the TBrac-2018 tournament
3. Select Setup->Rules
4. In Tournament Options, switch "Interface with BLS or BTM" to Yes
5. Select the "Link BTM or BLS" tab at the bottom of the page
6. Press "Select a BLS League"
7. Identify the league that you will be linking to and set the squad that you will import it to
8. Setup your tournament normally
9. Close the rules.
10. If you have not setup the lanes and dates for the squads, do that now.
11. Select Import->Import Linked Leagues and Tournaments
12. Press "Update Average for Selected Link".
13. Select the week that you will be importing from and press ""Yes, do it"
This imports bowlers, averages and scores. The import tool is designed so that the bowlers can be imported before there are scores, and again as you complete a game or all games.