Thanks for bringing this to our attention, paysagement. We can explore potential scenarios, including reviewing your company settings for tax rate selection and customer profile setup, to ensure everything is configured correctly. Let me elaborate on this further and share some fixes.
If you intend to add a tax rate when creating an invoice, please know that this can be due to the Default tax rate selection setup in your Company settings, as well as the configuration for that customer in their profile, which is set to a Default tax code of Out of Scope.

However, you still have the option to manually select a different SALES TAX rate during the invoicing process.

Additionally, please check in the Manage sales tax tab to confirm whether the Quebec tax rate has been marked as inactive. If it has, you'll want to activate it to apply it to your transactions.

If everything appears correct, we can open an incognito window in your browser to access the product with a clean slate. Depending on your browser, you can use the following shortcuts:
- Google Chrome and Microsoft Edge: Ctrl+ Shift + N
- Mozilla Firefox: Ctrl + Shift + P
- Safari: Command + Option + P

If you can add a tax rate for Quebec, please return to your regular browser and clear the cache for a fresh start. Additionally, switching to other supported browsers can also be worth a shot.
On the other hand, if you're referring to something else, it would be helpful if you could provide clarification. A screenshot would also help us better assess your situation and provide an accurate resolution to your query.
After processing your sales with the correct tax rates, I've included an article that'll guide you in filing your taxes in the future: File your sales tax return and record sales tax payments in QuickBooks Online. This offers guidance to help you avoid late submissions and additional fees.
Please keep us posted if you have further questions about sales tax and rates QuickBooks. We, in the Community, are always here to help.