Export Restrictions for Teensy 4.1?

Not necessarily a definitive answer, but the very last page of the i.MX RT1060 Processor Reference Manual includes the following boilerplate text:

Export control — This document as well as the item(s) described herein may be subject to export
control regulations. Export might require a prior authorization from competent authorities.

Mark J Culross
I suspect that any export restrictions may be related to the cryptographic hardware functions. Those functions are not documented in the standard data sheets. IIRC, you have to sign an NDA to see the specs for those hardware modules. I think Paul has signed the NDA and is keeping his promise in the PJRC forums and website documents. I've signed NDAs in the past and do my best to abide by their terms. The decision to relinquish absolute freedom to disclose in return for access to hardware and software specifications is something that every developer may face in the transition from commercial to open-source development.

I signed the mother of all NDAs in 1974 at the end of my naval service as a cryptologic officer. It was still affecting my ability to write a memoir for my family in 2018. You've not really gotten deep into NDAs until "Subject to Title 18, USC" appears in the text. In my case, they wouldn't even give me a copy of the NDA!
In Mexico, to order a Mouser Teensy 4.1 I had to fill out a questionnaire before they would allow me to buy it. Sparfun has a section indicating the export restrictions to which some of its items are subject.

Fortunately my teensy 4.1 is with me, helping me monitor the liquid cooling of my gaming PC
Mouser refused to send me (in Germany) a Teensy 4.1 some years ago. They even did not even get a chance to fill out a questionnaire. No problems with DIGIKEY (only the standard questions on purpose of purchase)