Personally, while I wouldn't say that mixed teams "don't work", they are much harder. Specifically for management.

The managers need to enforce that all meetings have to include remote workers. And I mean ALL meetings should include them, or at least give them the option of joining in. Managers need to avoid falling in the trap of "I didn't talk to them today so they didn't do anything", even subconsciously. Managers need to make sure that no decisions are made informally in an office without giving a chance to remote workers on the teams from having input or knowing they happened. Managers need to make sure that in-office people know how to use and work with the remote work tools, and remote workers need to be held to the same standards (no one-on-one calls and decisions without including all the in-office people, not just the one they are talking to at the moment).

It's not impossible by any means, I even work in a situation like that myself right now where about half the team is remote, and half is in the office. But having worked in fully remote teams and fully in-office teams before, I will say that it's much easier when it's not mixed.

One really kind of "unique" setup I have at a current job is an always-on zoom "meeting room" where team members will stay in all day sometimes (often any time we aren't working on something individually or deep in a problem). It really bridges the remote/office gap really well, because just like in an office any of us can just unmute and ask a quick question about something, kind of like leaning back to ask someone a question at another desk in an office.

The key for my team was a "remote-first" mindset. First, check on chat or e-mail. Then, if that doesn't work, head over to their desk to see if they're there.

(+1 to me for getting "their", "they're", "there" right on the first try!)

It's definitely possible - I would say that to be most successful you want to behave like everyone is remote all the time, which means remote access to meetings, not whiteboarding and leaving somebody out because they're remote, etc, and bringing in remote folks when in-person really matters.

Otherwise you'll eventually get silos depending on people's locations. That can work too if they're all kinda grouped in terms of work function but it's not as ideal as "treat everyone remote" for sharing information and productivity.

Yup, and I can confirm with another data point.

When the whole organization buys in to the remoting experience, it can work. Where I'm at, the default assumption is remote; be it home or another office since we're so distributed. So our way of working takes that into consideration.