Corner roundedness is personal preference in the Appearance page in COSMIC Settings. Similar to interface density.
It wouldn't be possible for us to build a platform toolkit, or the COSMIC platform itself, without a text editor or terminal. It would also be deeply embarrassing if we release our desktop without them. Imagine telling people they need to switch to a TTY or use a software center to install a plain text editor or terminal. It is thanks to the text editor project that we have first class text rendering across the Rust GUI ecosystem now. Without it, we wouldn't have been achieve proper bidrectional text rendering or ligatures. The text editor project also made the terminal possible, and now any application that we develop in the future can have proper text editing widgets and embedded terminals.
Sounds like voltage droop and/or a motherboard with faulty automatic "training" settings. I don't recall if the Ryzen 3000 had custom PBO curves, but tweaking this can fix it. Upping LLC and the SOC and CPU voltage slightly alternatively could help. Though I've had my most stable overclock by disabling PBO entirely and using a manual CPU multiplier.
You can generate documentation by running cargo doc and browsing the generated web pages in target/doc. There are also examples in the examples directory of libcosmic, as well as a design demo example which is a WIP.
libcosmic is an alternative toolkit for building desktop applications and layer shell applets. It wouldn't make much sense to build a toolkit only for ourselves. It's the best way to develop layer shell applets for COSMIC, and other Wayland compositors that support the layer shell protocol.
It's difficult to say for sure with certainty what the issue is without trial and error. I would expect that the motherboard's manufacturer would make sure that their board can successfully pass all tests with the standard JEDEC spec for DDR4 (2133 MHz).
Since you say that you've tried different RAM kits, another alternative could be the cleanliness of power from the power supply. Perhaps there is intermittent voltage droop, and you need to experiment with the Load Line Calibration settings to adjust for vdroop between idle and load. Disabling frequency boosting and manually setting the CPU frequency could help check if it's related to that. PBO curves might be undervolting too much while idle.
That's already not possible on GNOME because some GNOME applications hardcode their theme, others use libadwaita, some use GTK4 without libadwaita, some use GTK3, and there may still be a GTK2 app lingering around here and there in the repos (ie: GIMP).
Few people are going to care that there's a GTK application installed on their COSMIC desktop. COSMIC will automatically generate GTK3/4 themes to match the system theme. We may even automatically generate a libadwaita theme, so it will look "same enough".
Iced is a lower level GUI library, similar to what GDK is to GTK. We built our own COSMIC-themed GUI toolkit around iced, which is called libcosmic. As we've gotten more and more widgets and application logic developed, actual application development with libcosmic is a breeze. Even if you do have to create a custom widget, it's much easier to creating custom widgets in GTK. We're able to develop much faster than we ever could with GTK now.
Yew and Leptos aren't comparable since they're not native GUI toolkits. These are for web developers rather than application development. It wouldn't be possible to use this for developing layer shell applets for COSMIC, either.
It's been explained 100 times ad nauseam over the last two years. Go read comments from previous months' updates if you want to catch up.
As for cross-platform compatibility, this should not come as a surprise because everything is written in Rust, and the libraries we use are already cross-platform by default in most instances. Supporting multiple platforms takes almost zero effort on our part. Especially when we could design something from the ground up that's easy to adapt.
None of what you stated makes sense. Most people are not using exclusively GNOME applications on GNOME, or exclusively KDE applications on KDE. Like with elementary OS, most people are running applications like Steam, Spotify, Discord, Zoom, Slack, etc. Plenty of people are using Qt and KDE applications on GNOME, or GTK and GNOME applications on KDE. You think no one uses Krita or Scribus on GNOME, or GIMP on KDE?
Thanks to Flatpak, you might even be running elementary applications on your system. Even Windows back in the late 90s and 2000s was full of desktop applications with custom proprietary interfaces. Nowadays everything's becoming a web view bundled with a Chromium runtime, and you're more worried about a COSMIC app ecosystem having a different UI from GTK?
COSMIC is a good thing because it's a standardized and open source cross-platform native desktop toolkit. People can create themes for it, and those themes can be bundled alongside GTK and Qt/KDE themes. Due to the nature of how Rust libraries are developed and linked, COSMIC applications are mostly statically-linked, which even makes it trivial to put them on a USB drive and bring them to any PC.
I'm not sure why you think this is unique to COSMIC or elementary OS. Do you not realize that this is true of all operating systems? Look at Steam, Spotify, Discord, Zoom, and Slack for starters.
I don't think you can say that because we haven't published our design language yet. Only a handful of design mockups have been published so far. The screenshots here are not design mockups but a work in progress implementation. Hence the "In-progress" part of the title.
Rounded corners are a user preference in the Appearance page in COSMIC Settings.