The Brief: "Wallet" is a response to male chauvinists. The term means these men are only good for their money.

DEEP DIVE
“Wallet” is a term used to refer to men. It means they are only good for their money. According to Urban Dictionary‘s April 25 entry, the term is used in response to male chauvinists calling women “dishwashers.” TikTokers have adapted the phrase, “OK, wallet” to shut down men they see as the aforementioned.
The term “wallet” began appearing on TikTok in April 2020. It can be found in the comments section and even the topic of videos.
Here’s a TikTok video called “Dear Wallets:”
@bittnia I put a lil definition for “wallet” at the end just in case 🥰 + this is about a lot of gross situations I’ve seen on this app recently 😤 EatEmUp
Another video referencing the term “wallets” is this “This Is America” TikTok video.
@mynameisseannotseen Life as a white, straight, Christian male. We ARE oppressed #thisisamerica #fyp #foryoupage