Thanks for asking this matter, mwhittington.
The Profit & Loss Budget vs. Actual report by default shows all the accounts (active or inactive) associated with the budget in a given period. While there isn't a way we can filter it to remove the inactive accounts from 20 years ago, you can export the report and manually remove the inactive accounts.
To do this, just click the Excel button and choose to Create New Worksheet.

In case you encounter issues when exporting the report, you can visit this article for the steps on how to fix it: Fix export to Excel issues in QuickBooks Desktop.
You may also find these resources helpful when managing reports in QuickBooks Desktop:
We continue making improvements with the product and while doing so, I want you to be updated with the new features added in the software by following the steps below:
Here's how:
- Go to the Help icon.
- Click New Features.
- Choose either New Feature Tour or What's New.

Another way to be updated to the latest future release in QuickBooks Desktop is by visiting this website: QuickBooks Updates: New QuickBooks Accounting Software Updates.
Please leave a comment on this thread if you need anything else. We are always around to help you some more. Take care.