To combar spam I'd imagine. Is there no possibility to reach and use a temporary email service or smt?

I don't think a country could blanket ban every email provider that doesnt take emails as it's an open protocol; anyone can host an email server within seconds.

But you can use another lemmy instance that doesnt ask for email. It will mostly work the same way. You can also see the post contents of groups through other social media that uses ActivityPub (like mastodon)

It's mostly to combat spam. I created a lemmy account with an obviously bogus e-mail account, hopped on matrix and reached out to the instance admins and they activated my account manually after I asked nicely.

Tell your friend in a dictorial country that Lemmy.ml has pro dictorial leanings and is probably not the best instance for someone who is feeling oppressed.