QuickBooks depends on the third-party app you're using. Since you're unable to link your Shopify account to QuickBooks Online (QBO). I suggest contacting their support if they're currently having maintenance, Chris.
If everything's fine, I recommend troubleshooting your browser to ensure a successful integration. Sometimes, cache-related issues can cause QuickBooks to load incorrectly.
Let’s start by accessing QuickBooks in incognito mode or a private window by clicking the three-dot icon in your browser.

If this works, you can clear your browser's cache, cookies, and any temporary files that may have caused the malfunctions. Alternatively, you might try using other supported browsers to ensure QBO runs efficiently.
Also, you can explore our QuickBooks Live Expert Assisted team. They specialize in streamlining transaction sorting and can help optimize your financial management and accounting workflows.
If issues persist, please let us know, and we can explore further solutions together.