May I know what is your bank's name? Several reasons might be causing issues with linking your bank account. I'm here to provide you what are some of these and guide you on how to sort this out, seedalls.
You'll have to make sure you're using the correct URL found on the official website of your bank to successfully link your bank. This can be seen under your bank's name. I've added a screenshot for your reference:

Secondly, ensure to disable any pop-up blockers or browser extensions that might be interfering with the page functionality.
However, if you're still experiencing the same issue, we can proceed with troubleshooting steps to fix this.
You can log into your account using incognito mode. This doesn't store browser history giving you a clean slate and often resolving browser-related issues. Here are the shortcut keys:
- Google Chrome: Ctrl + Shift + N
- Mozilla Firefox: Ctrl + Shift + P
- Safari: Command + Shift + N
- Microsoft Edge: Ctrl + Shift + P
Once done, check if you're able to link your bank. If so, go back to your main browser settings and clear the cache. This usually resolves performance issues, and fixes loading and formatting errors.
If the problem continues, you can switch to another supported browser.
You may also want to know how to split transactions to organise your expenses, and track income. Go through this article for more details: Split Transactions in QuickBooks Sole Trader.
Furthermore, QuickBooks downloads the latest transactions and categorises them based on how other customers categorised similar transactions. To give you more information, check out this article: Categorise Bank Transactions in QuickBooks Sole Trader.
You can mention me in the reply below if you have any other questions or concerns when linking your bank. Remember, I'm always here to help you anytime.