Hello, I have the same problem.
I add 32gb ram to my iMac 2020 27 "
After installing the ram, I waited about 2 minutes for the machine to finish booting. And currently my iMac is running with 40gb ram.
I have read this message on the Apple’s support page:[br]
''Note:'' Your iMac performs a memory initialization procedure when you first turn it on after upgrading memory or rearranging DIMMs. This process can take 30 seconds or more, and the display of your iMac remains dark until it’s finished. Make sure to let the memory initialization complete.[br]
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