Hello 391972, 

If you haven't tried running the Condense Data Utility, as mentioned by Fiat Lux - ASIA, you can follow the steps below to optimize your QuickBooks 2020 performance. 

1. Go to the File menu.
2. Select Condense Data under Utilities.
3. Choose the  best option for your company by keeping all transactions.
4. Click Next. Then, follow the on-screen instruction to complete the process.
   

Also, you can check these articles where you can get additional information on how to let the program works well:

• Recommendations to resolve performance issues. 
• Resolve QuickBooks Desktop performance issues: Manage your computers. 

If the same thing happens, I would recommend getting in touch with our support team. They have the ability to look into your specific account in detail, see what's going on and even screen share with you if necessary. Here's how:

1. Go to the Help menu once you open QuickBooks.
2. Click QuickBooks Desktop Help or press F1 on your keyboard.
3. Select Contact us button. 
4. Enter a short description of your concern in the Tell us more about your question box. 
5. Hit Search. Select Start a message.

Also, you can check the links below for additional reference about QuickBooks Desktop 2020:

• What’s new in QuickBooks Desktop 2020.
• Release notes for QuickBooks Desktop 2020. 

Comment below if there's anything else you need. I'll be here to help in any way that I can. Stay safe.