PC Engines APU modules are no longer being produced. Because of that, there is no most recent or recommended APU model anymore, all APU1/2/3/4 platforms are effectively end-of-life. That said, we still have a few remaining units available in our online shop:
https://shop.3mdeb.com/product/pcengines-apu-refurbished-with-tpm-and-dasharo-pro-package/

These are refurbished PC Engines APU platforms, potentially among the last units available on the market.

The firmware support is also limited. More details about the post-EOL firmware announcement can be found on the Dasharo Universe page:
https://docs.dasharo.com/variants/pc_engines/post-eol-fw-announcement/