I didn't say Biden's tenure was destabilizing. What I'm suggesting is that his tenure has less stable international relations than Trump's did. I'm not saying that either man carries all or even primary responsibility for those circumstances, but if someone wants to claim a president was destabilizing, it's hard to support that argument when situations were more stable.Hmm, you didn't explicitly, because that would have required substantiation. What you did instead was list it among various other things that happened during Biden's tenure... as evidence for why his tenure was destabilising.
To your other question: the US and Iran are adversaries, and have been for quite a while. Open opposition from the US isn't destabilizing, rather it quite stabilizes the status quo. The status quo is open opposition between the two nations.