Apple ID Verification Code message shows up randomly

I'd make sure to go thru every step at If you think your Apple ID has been compromised - Apple Support

Here's more, some of which is not in Apple's documents referenced in my previous post. I am therefore posting it separately since it is not part of Apple's official guidelines. However, it probably has more specifics to actually aid in identifying bogus messages.

- Apple e-mails address you by your real name, not something like "Dear Customer", "Dear Client", or an e-mail address*.

- Apple e-mails originate from @apple.com or @itunes.com but it is possible to spoof a sender address. "Apple email related to your Apple ID account always comes from appleid@id.apple.com." - About your Apple ID email addresses - Apple Support

- Set your email to display Show Headers or Show Original to view Received From. Apple emails originate from IP addresses starting with "17.".

- Mouse-over links to see if they direct to real Apple web sites. Do not click on them as this just tells the spammer they have a working e-mail address in their database. If you are unsure, contact Apple using a link from the Apple.com web site, not one in an email.

- Phishing emails may include account suspension or similar threats in order to panic you into clicking on a link without thinking. They may report a fake purchase in order to infuriate you into rashly clicking on a false link to report a problem. March 2018 post by Niel https://discussions.apple.com/message/33129140#message33129140 - "Emails saying that your Apple ID has been locked or disabled are always phishing. If one actually gets disabled, its owner will be told when they try logging into it instead of through email."

- Apple will not ask for personal information in an e-mail and never for a social security number.

- Scams may have bad grammar or spelling mistakes.

- Apple will not phone you unless it is in response to a request from you to have them call you.

* Exception: https://discussions.apple.com/thread/8483395?answerId=33701414022#33701414022

Forward email attempts as an attachment (in MacOS Mail use the paperclip icon) to: reportphishing@apple.com then delete it.

If this is with regard to a supposed purchase, this Apple article has relevant information and web links for checking if you really have made a purchase or paid for a subscription: If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement - Purchases made under Family Sharing might be charged to the organizer's card but will not appear under the organizer's purchase history or subscriptions. Ask family members about those or check your receipts. --> If you see 'apple.com/bill' on your billing statement - Apple Support Apple will email a receipt to the Family Organizer if a purchase is made on a card held by the Family Organizer. This will have the Apple ID of the purchaser, which you should recognize, but won't have specific about what was purchased.

Read this link "If you think your Apple ID has been compromised" --> If you think your Apple ID has been compromised - Apple Support

Also make sure you are using "Two-factor authentication for Apple ID" --> Two-factor authentication for Apple ID - Apple Support

The two factor authentication verification pop up would only appear on trusted devices if someone is trying to sign in. Do you have a PC that could be trying to auto sign in maybe?

As for pressing OK, you are fine to press it as you are just acknowledging you are done with the code, nothing more.

A lot of this security stuff has two faces. It can be real, but scammers and phishing send out messages that look like Apple messages, but are really trying to get you to enter your account information on their fake web sites made to look like Apple.

Scams (e-mail, text messages, and phone calls) are getting very good at closely imitating true Apple communications. Always be cautious. These support articles have some guidelines:

About identifying legitimate emails from the App Store and iTunes Store --> Identify legitimate emails from the App Store or iTunes Store - Apple Support

Recognize and avoid phishing messages, phony support calls, and other scams - Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Avoid scams when you use Apple Cash --> Avoid Apple Cash scams - Apple Support

Apple 'How to identify, avoid, and report phishing' video--> https://youtu.be/SR3Z3fXXjfw

If you are uncertain about a message and a resource provided in that message, do not click on any links in the message. Try to independently verify the resource by going to a support article page on apple.com and use the instructions in the article to verify though Apple itself, or your Apple device features such as Settings or an Apple app, what the message is claiming. To ask Apple start at this web page: Official Apple Support

Forward email attempts as an attachment (in MacOS Mail use the paperclip icon) to: reportphishing@apple.com then delete it.

Nice detective work! I would send this as feedback to Apple so their dev's are aware, which they may be already. Product Feedback - Apple