The supported processors are listed in the publicly available source code on GitHub.
Ghidra and IDA Pro both support quite a wide variety of architectures and processors. It's hard for me to tell which one supports more, and I am not sure how meaningful that kind of comparison is.
For more information, see this presentation and associated materials:
Quoting the Ghidra Wiki,
What processors are currently supported?
X86 16/32/64, ARM/AARCH64, PowerPC 32/64/VLE, MIPS 16/32/64/micro,
68xxx, Java / DEX bytecode, PA-RISC, PIC 12/16/17/18/24, Sparc 32/64,
CR16C, Z80, 6502, 8051, MSP430, AVR8, AVR32, and variants of these
The latest IDA pro supports more than 60 families of processors....