After SXMO, the DWM-on-phone mod that became popular for its practical minimalism with the PinePhone, and the lesser known ExpidusOS XFCE-based shell, many of the traditional lightweight Linux desktops are receiving touch-friendly adaptions. A relatively new project, AVMultiPhone, is loosely based on the popular MATE desktop, which continues the GNOME 2 legacy experience with modern libraries such as Gtk3.
However, there is more to this than standard MATE. First and foremost, the touchscreen experience appears to be nearly complete, and generally usable. Secondly, a series of applets and configurations was added to ease the integration of details such as touchscreen keyboards.
The desktop can be tested as part of the "AVMultimedia" distribution, which is available for download on SourceForge in a PinePhone image, and was developed by the Swiss firm Archivista GmbH.
But apart from the above, not much is known about this desktop yet. The blog post announcing a version 2, linked below, explains the project in depth, but the source code for this pre-alpha does not appear to be immediately available online, and the author suggests buying a book, or donating to their bank account to motivate any possible future development. Which, admittedly, is a peculiar approach to open-source.
Via LINMob (YouTube)