When you submit a normal GST/HST return, you can claim ITCs (input tax credits) to recover the sales tax you paid while doing business. When you use the quick method, you can’t claim ITCs for most of your purchases. The portion of the sales tax that you keep is supposed to make up for GST/HST that you paid on your purchases. This CRA page has a list of the items that you can claim ITCs for, when using the quick method: https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/rc4058/quick-method-accounting-gst-hst.html#P214_17670
If you have TurboTax Live Assist & Review, here is how to talk to a Tax Expert: https://turbotax.community.intuit.ca/community/navigating-turbotax/help/i-m-using-turbotax-live-assist-review-how-do-i-talk-to-a-tax-expert/00/873764