In a world where the vast majority of all-in-one and small form-factor PCs rely on proprietary motherboards, the Thin Mini-ITX form-factor is not particularly widespread, making it difficult for PC shops and DIY enthusiasts to build AIO and SFF computers. However, Thin-Mini-ITX motherboards are not going the way of the dodo, and ASRock's recently announced AM4 X300TM-ITX is a good example of continued interest in the platform.
The ASRock X300TM-ITX platform combines compatibility with AMD's Ryzen APUs (up to Zen 2-based Ryzen 4000-series) with an expansive feature set, including a USB 3.1 Gen 1 Type-C connector, a COM port, and an LVDS header, all of which are rather exotic for what are typically inexpensive Thin Mini-ITX motherboards.
Furthermore, the COM port and LVDS header make this platform useful for commercial systems that actually need these types of connectivity. ASRock doesn't officially position the motherboard for business or commercial PCs, but it does support AMD Ryzen Pro APUs, so you can certainly use it to build a PC with Pro-class features.
As the name suggests, ASRock's X300TM-ITX motherboard is based on a rather dated AMD X300 chipset that was originally designed for entry-level systems aimed at overlockers, but it still supports the vast majority of AMD's APUs with an (up to) 65W TDP (except the upcoming Ryzen 5000-series processors). The board also supports up to 64GB of DDR4-3200 memory across two SO-DIMM memory modules, an M.2-2280 slot for SSDs with a PCIe 3.0x or a SATA interface, and one SATA connector.
ASRock aims the X300TM-ITX motherboard at thin entry-level systems that don't typically use discrete graphics cards, so it doesn't have a PCIe x16 slot for an add-in card. Instead, the platform uses AMD's integrated Radeon Vega GPUs. Meanwhile, the LVDS header supports resolutions of up to 1920x1080 at 60Hz, whereas the HDMI 2.1 connector supports HDCP 2.3. There is no word about DisplayPort support over the USB Type-C connector, and you should be aware that HDMI-to-DisplayPort adapters may not work with all displays.
ASRock's X300TM-ITX has an M.2-2230 slot for a Wi-Fi card along with a GbE port. It also has USB Type-A connectors as well as a 3.5-mm audio input and output.
The platform is already mentioned on the manufacturer's website, so it should be available for purchase soon. Unfortunately, ASRock didn't touch on pricing in its press release.