Can’t move emails to folders

Assuming you are using an inbox in Apple's "Mail" app:

You might give Apple's 2024 method a try:

Move your email messages to a mailbox

1. Go to your Inbox in Mail.
2. Tap Edit in the upper-right corner.
3. Select the email messages, then tap Move.
4. Tap Move Message.
5. Choose a mailbox to move the email messages to.

From: Use mailboxes to organize email messages on your iPhone or iPad - Apple Support

Re: "Can’t move emails to folders : I’m on an iPhone 12 mini iOS 18.0.1."

Wondering if updating to the newest iOS version may help:

(Please note: It is always wise to back up your iPhone data before updating:)

Apple support's article: About iOS 18 Updates - Apple Support says iOS 18.1.1 is the newest version

and

"This update provides important security fixes and is recommended for all users".

(NB: With the earlier update iOS 18.1 Apple introduced "the first set of features powered by Apple Intelligence, the personal intelligence system" )

You can always go to Settings > General > Software Updates to see what's available.

Thank you for confirming just when Apple's method of moving emails fails for you on your iPhone's 12 mini's iOS 18 version.

You may want send feedback to reach those who work behind-the-scenes at Apple. Although they will likely not reply, your feedback will reach those who can make changes if others are are experiencing a similar issue. Eg: Apple can see which iPhone models, and which iOS versions are affected, so a future update may address the issue, for those experiencing it.

Web-form for feedback: Feedback - iPhone - Apple