I can help set up your QuickBooks Online's log in credentials get remembered in your browser's memory.
For QuickBooks Online Windows app, it will remember the user ID after signing in. Please check the Stay Signed In box in the sign in page.
If the app, won't remember your login credentials, it'll be a good idea to uninstall and reinstall the application. Here's an article for more info: QuickBooks App for Windows and Mac.
Let us know if you have any questions. Thanks!