The built-in Jitsi integration lets you create a voice chat call via a single button click. You can also put those call links in a channel description if you like.

We do have plans to make the integration offer some additional ways to jump into a call, and have been talking about adding video chat. But our focus has been on building the best text chat possible, given there are multiple actively developed FOSS video call systems that we can integrate with.

Jitsi used to be so frictionless, but now that their public instances are a bit more locked-down (understandably...) I wonder if developing a deeper first-party integration would be sensible.

If you are selfhosting zulip, what prevents you to selfhost jitsi?

I have in fact done that before several years ago, though when I looked at it again late last year it seemed more complicated.

Looks like it has integration with Jitsi Meet https://zulip.com/integrations/jitsi

in slack and discord i don't need another app i just hit the huddle button (in slack) and join a voice chat room in discord.

This is the problem with pitching zulip to this audience. The original thing that got gamers to switch to discord, it was their original and probably still is their primary target market, was a single login to a huge universe of voice chat rooms. Before discord gamers were setting up/renting teamspeak and ventrillo services (that were voice chat only). Hell for the first couple of years of using discord with my gaming group the only thing anyone ever posted in text was what time they were going to be on and what game they wanted to play.

I would say the main thing that got people to switch to Discord was the fact that voice chat was free, paid for by VC money.

sure but also that you didn't have to pass around your teamspeak/ventrillo information to every rando you wanted to play with, less friction in discord with invite links etc

I have never created an account nor logged on to use jitsi.