As a guide, if famously fair and balanced Fox News or the German far(t) right media outlet Nius calls anything anything, it's probably not that. Or at the very least, it's a convenient reduction of facts to something that fits their talking point.
Mastodon isn't a platform in the same way Xwitter is. That's a centralised platform, Mastodon is many independently hosted instances choosing to federate with each other. Among those instances you'll find those tolerating asshole opinions of all kinds. And then other instances de-defederate from the collective. So labelling all of Mastodon antisemitic or anything else speaks to a lack of understanding on behalf of the person making that claim.