I'd assume separate is more popular nowadays..? (Instead of converting gi to nogi when it gets too warm, which I guess is the old school alternative.)

We have it separated the same way in the schedule, Gi (IBJJF-rules, competition style jiujitsu) and Submission Wrestling (ADCC rules). Also had pure self-defence jiujitsu for a while, but it wasn't very popular.

We got a few brutes who only train no-gi and people are allowed to come to the gi classes without the gi, but typically they only come when they know in advance they get at least one gi-less partner so no civilized clothed person has to end up training with them, unless they want to. If the technique taught needs a gi, they just drill they own stuff (mat space is quite big) and basically join the others for warm-up & sparring rounds. Also we have one no-gi class where people are encouraged to come with a gi on if they prefer it (it's more popular) but I don't think this right is often acted upon.

We have separated classes but those no gi people just appear out of nowhere at every class and I'm too nice to send them away.

Monday is Gi only but we don't send people away if they don't have one.
Tuesday and Saturday are 2 hour sessions where nominally the first hour is NoGi and the second hour is Gi. In practice, most people do both hours and don't get changed in between so it ends up reflecting peoples preferences. I usually wear the Gi for the simple reason that if people can break my technique by grabbing it, i want them to. Better to find out in training than competition.

Our gym has separate classes for gi and no gi depending on the day of the week.

Same. Occasionally we do 1-2 exclusive gi classes per week (gi comp season). If someone shows up nogi they can borrow a jacket from gym's rack.

we got classes for each but im pretty easygoing
only thing i say is if you show up without gi you cant learn using it...
if the school grows and we get full gi and nogi classes i might get more strict tho...

now for the techniques i always show everything,
even damn heelhooks in the gi once in a while if i feel like it (and that not just by the way but with focus on the gi pants friction that makes heelhooks extra devastating)
but i always explain what is when allowed and what not and tell them if they compete they should roll under the rules of the comp they are going too

i even show shit thats never allowed like pulling the back of the gi over ones head to blind em or even wrap it around their neck to chocke them like with a plastic bag lol

im not one of those hardcore self defense guys but i just like to display all possibilities and make people openminded

in the end everyone always does the same shit anyway... its more fun to spice things up a bit :)

I've always been pretty strict on this. If it's a gi class, I don't want anyone to participate without a gi. It's pretty annoying if I'm teaching some gi details and someone ends up with a partner who was too lazy to follow the directions and then they can't practice what I'm teaching that day. In the beginning (15-20 years ago), I was more loose about it, but once people found out they could get away with it, I suddenly had 1/3s of the gi class not wearing gis and it was impossible to plan what to teach. Especially for a competition heavy gi team, it's extra annoying.

Nogi is for nogi classes and open mats in my shop.

Our gym usually has a few extra gis for those newer guys that don't have one yet.

At my place, if you're new, then not wearing a gi in a gi class is ok, but I expect everybody to have a gi within a week or two of joining. Otherwise it affects other people's training, because they don't get to practice the technique properly, plus it makes sparring awkward.

But yeah, allowing both seems to work well at BJJ Globetrotter Camps when the technique isn't specific to gi: Priit and Chris P never limit their classes to gi or nogi, not sure if it's the same at 'normal' classes in their schools.