Thanks for joining this thread, stpi. I appreciate your detailed information.
 

According to our Order an Intuit QuickBooks Payments MagTek card reader article, MagTek card readers still work with QuickBooks Online. The article was last updated in January 2024.
 

As for why you're not seeing an option to swipe cards with your MagTek card reader, I'd recommend getting in touch with our Customer Care team to troubleshoot why the option isn't displaying. As the article linked above covers, these card readers do function in QuickBooks. The agent will be able to pull up your account in a secure environment, conduct further research with you, and create an investigation ticket if necessary. That way this can be investigated further by our Product Investigations team as to why the option isn't there.
 

They can be reached while you're signed in.
 

Here's how:
 

1. Use the Help (?) icon.
   
   
    
2. Click Contact Us.
   
   
    
3. Enter a description of your situation in the What can we help you with? field, then hit Let's talk.
   
   
    
4. Select Start messaging or Get a call.
   
   

Be sure to review their support hours so you'll know when agents are available.
 

The article about MagTek card readers also confirms that they function in your Merchant Service Center as well. You can try accessing the QuickBooks Payments account and see if your option to swipe cards is visible in there for the time being:
 

1. Sign in to your Merchant Service Center.
2. Go to Processing Tools, then Charge a Card.
3. Complete the necessary fields. Comments you add are only visible to you and the cardholder.
4. After processing your payment, you'll see a confirmation screen. You can select to Print, E-mail, Void, or Done.

I've also included a detailed resource about processing payments which may come in handy moving forward: Process payments in the Merchant Service Center
 

Please don't hesitate to send a reply if there's any questions. Have an awesome Friday!