You can create endless Gmail accounts for free and google has several different 2fa options to choose from. So you could make one ‘2faClassDemoEmail@gmail.com’ or have each person on their own device create dummy Gmail addresses like ‘StudentName2FADemo@gmail.com’ and have each student go through the process individually. They would only be temporary in that you’d just stop using it after the class and google would eventually get rid of it(maybe?) After long enough without any use. I don’t think you’re going to find something that just generates dummy 2fa codes for demo purposes.
Breh that attitude is 100% self defeating and contributing to the struggle you’re having connecting with people both irl and online. Neurotypical people aren’t all just good at everything you’re not. They struggle with some things just as much as non-neurotypical people do. If there’s one piece of advice id ask you to hear is not to focus on finding a date or someone to be with. Focus on developing your own independent interests and engage with the communities around those interests. But go into it with only the desire to connect with people, whatever form that takes. Do that enough times and you should start finding people who might just be interested in spending time with you rather than just sharing an activity together. Dating apps are dehumanizing and are for the hot and naturally charming, definitely not worth engaging unless you have an abundance of confidence and a tolerance for being value judged on every aspect of yourself.
Also, just going to the power off slider screen will force a passcode reentry.