The lack of transparency in the industry (Apple is not alone), as well as shifting sands, is making things difficult for users.
Apple
tightened up the requirements for their 7.5W "fast" charging profile with iOS 13.1.
You need to
search for a charger that supports the Extended Power Profile (EPP).
Qi is an open standard, just like USB is, but manufacturers are piling on their own proprietary methods for faster charging, which while sanctioned (PDDE), does not help the consumer.
It's a repeat of the wired situation where QC, PD, and a litany of other fast charge standards from the Chinese brands put the onus on users to sort out which combination will achieve the desired goal.
The best you'll be able to do is note whether a charger you may be interested in is said to fast charge iPhones, and then engage in some trial/error to see if that claim is true. Few, if any, use the technical terms like EPP in their marketing, so you'll have to independently verify that, and hope that Apple, Google, Samsung, and the like haven't changed the rules in the meantime (or the future), and it works.
If it doesn't prove to, send it back, and make clear that the reason is because it doesn't live up to the claims.