How to get an Apple seed invite?

https://appleseed.apple.com/sp/welcome

You can initiate the process by following the steps in the "Requirements" section in the link I provided above. Participants are selected and invited based on the profile submitted by the applicant.

But at this time the site has a notice "We are not seeking new participants. You must have an invitation in order to log in."

FYI, the requirements are for your participation once you’ve been invited and have accepted the invitation. You complete the profile for the - only for seed participants - discussion area and download instructions/links. The discussion area is for seed participants only and also include strict non-disclosure terms; public betas do not have a discussion area.

Since it is an invitation only program, Apple will contact you if they are interested in inviting you.

However, the public betas are available to anyone - be aware that as a beta participant, you are not allowed to discuss anything about it with anyone, so your only recourse would be to file a bug report with Apple which will not help you troubleshoot. You will be on your own.

Nice catch.