Hi there, twowksearly.
Can you tell us if there's an error message when you try to upload the logo? This is for me to check if there's an open alert that's related to your concern.
I also appreciate you letting us know that you already made sure the file is using the correct format as well as clearing your browser's cache.
Since you've already checked those things, I recommend reaching out to our support team. They can take a closer look at your logo and help figure out why you're unable to upload it.
Here's an article on how to reach out to them: Contact QuickBooks Self-Employed Support.
For more tips on using QuickBooks Self-Employed (QBSE) to track your business transactions, check out these articles:
If you have any further questions or need more assistance, feel free to post a new question in the Community. We're here to help.