Gmail scans emails for receipts and collects these automatically.

The purchases are neatly listed on a hard to find Purchases page on Google's My Account portal.
https://myaccount.google.com/purchases
The author of the article thinks this is terrible and in some aspects, he's probably correct.
I thank him for bringing this fact to my attention and am happy that I know know of a central point
where I can access my purchases. I've added a shortcut of this link to my bookmarks bar.
You may well agree with Mr. Brinkmann's view on this topic.
https://www.ghacks.net/2019/05/18/gmail-tracks-all-your-purchases-and-it-is-difficult-to-delete-them-and-impossible-to-stop/