firmware

Which firmware can be used

Marlin
Klipper
RRF

What does the board need that it can be used?

32bit
6 Stepper Motors or 5 Stepper + 1 Toolboard
Neopixel Support
3 Thermistor Inputs (Hotend, Heated Bed, Enclosure)
min 3 fan outputs

Some Boards to choose from (incomplete list)

Fysetc Spider
BTT Octopus
Mellow Fly Board
BTT E3 RFF + IDEX
BTT SKR Pro
SKR 2.0 + BTT Mot Exp
Duet 3 Mini 5+ + 2+ Addon or + Toolboard
Duet 3
Fysetc S6