Until there is anything formal from Apple allowing alternative browser engines I’d wouldn’t really expect too many updates from Firefox on their custom engine project.

Firefox on iOS is in the end not a lot more than a wrapper to Safari. And I’m not happy with that.

Don't buy Apple products then. Apple's policies around that issue are known since many years by now.

Do somebody know where we stand with that ? Is it abandoned, still in progress ?

Apple for now does not allow that. There were rumors this could change but only rumors.

There are a few rumours that Apple might drop the WebKit requirement soon, due to some laws adopted by the EU, however there has been no official response or comment by Apple so far.

If you like privacy and freedom, you could use Android (degoogled, obviously). I understand the EU is trying to force Apple to become better, but it's still a walled garden much more than Android is, or aspires to be.

As far as I know, companies don't have to comply yet with the Digital Markets Act. That's most likely the reason why the WebKit restriction is still in place.

I google it every so often, but I think it’s dead or a private project for now

I'm looking forward to it too. They have mentioned a few times in the past they wanted this but I think as long as it's not officially possible they are not going to post progress reports. Without having any evidence I'm pretty sure it'll happen but I can understand Mozilla not making any promises until it's possible for sure.

Furthermore it will in all likelihood only be allowed in markets that legislate for it which ultimately will probably be everywhere but not to start with.

We just have to be patient.