The big obvious one is web-based tooling. Your information & settings are stored on a server and you use a web browser to view it via whatever device you're on. For more locally based workflows, we have networked filesystem protocols, automatic syncing between systems, that kind of thing. It's not a 1-1 equivalent of running a remote program and viewing it locally obviously, but it gets the same job done, in a much more useful & flexible manner than X forwarding did.
For example, the remote mail client usecase I was replying to is simply done with a webmail client today.
I don't really feel like web interfaces or syncing are really a substitute tbh, and I'm not sure how they're more flexible. ssh -> run -> gui opens, and the program itself doesn't need to be designed differently to work
> and I'm not sure how they're more flexible. ssh -> run -> gui opens
But this doesn't work on your phone, or on a Windows or macOS device, right? That's what I meant by flexible, X forwarding fits a pretty narrow set of usecases, while on the other hand keeping programs on the clients and data centrally located on a server allows for a whole lot more options for how to interface with that data.
(To be clear, nothing wrong with X forwarding! It's a cool tech and I'm glad you have a use for it! I'm just arguing that it's fine for Wayland to not try to support that kind of thing, because we've got other ways of working remotely now.)
Phone I didn't know, but the sibling comment interests me. Windows, it works fine on local WSL but for remote yes you do have to have something like mobaxterm running. Not a big deal to me. Mac, I thought it just worked? It used to at least for me, but the last mac I owned was on snow leopard, so I wouldn't be surprised if they decided it wasn't the Mac Way to do things.
Most recently I used X forwarding to manage some LVM disks. I usually like using cli, but for me it's just easier to deal with disks with a GUI. Shy of setting up a full remote desktop, which I've had a lot of trouble with getting to work reliably, what's a better option here for an arbitrary disk program?
X servers are available for phones, Windows, and macOS. X interfaces not designed for phones can be difficult to use on phones. But web interfaces not designed for phones can be difficult to use on phones.
There is not a web tool for every use. And web tools are not better for every use.
For example, the remote mail client usecase I was replying to is simply done with a webmail client today.