Uconsole bigger one - https://www.clockworkpi.com/home-devterm

Beepberry - https://beepy.sqfmi.com/
https://liliputing.com/beepberry-is-a-79-hackable-pocket-computer-kit-with-a-blackberry-keyboard/

Colorberry - https://www.elecrow.com/colorberry.html
https://github.com/hyphenlee/colorberry

PC Pilet old but cool looking one - https://soulscircuit.com/pilet
https://www.raspberrypi.com/news/pilet-mini-pi-5-modular-computer/

ESP32 - ESP32 is a SoC, example of handheld using it is the LILYGO T-Deck Plus - https://lilygo.cc/products/t-deck-plus-1
https://linuxgizmos.com/updated-t-deck-plus-an-esp32-handheld-device-with-gps-and-lora-support/

Mecha Comet with the switchable keyboards - https://mecha.so/comet
https://www.geeky-gadgets.com/modular-linux-handheld-mecha-comet/

Some links to help checking out the handhelds mentioned.