After a week of spotting the new AMD AGESA through MSI's updates, (which is often quite fast with this kind of BIOS update), AMD has now formally announced the new microcode, as reported by TechPowerUp.
Updates include faster POST with certain Micron DDR4-3200 RAM and some fixed memory errors with Realtek onboard Ethernet. The Ryzen 3 Pro 2100GE had an issue with PCIe lane configuration that has been fixed, and the new AGESA also supposedly provides better PCIe stability.
All things considered, these changes aren't huge but should fix annoying nuisances for a small group of affected users. Therefore, most of us needn't rush to install the new microcode. However, for those affected by the issues, it can be quite a nuisance that motherboard vendors can take a long time to implement the changes in a new BIOS.
The prior AGESA microcode, version 126.96.36.199, offered a few more interesting changes. These included faster boot times but also made it possible to run a 1st-generation Ryzen CPU on an X570 motherboard.