Regardless, I never use unpowered USB hubs with anything other than a keyboard + mouse or a wireless mouse + 1x USB thumb drive. And I only use them with my laptop.
For farming, I only use powered USB hubs. Just assume you are running into a power limit issue and assume that you will need to get a powered USB hub of some kind.
I also use a raspberry pi 4 for farming Chia, but I’m using only 3.5 inch external powered drives. I have 7 external HDDs connected to a unpowered TP-LINK 7 port USB hub and I do not have any problems.
My idea was the same, but unfortunately I couldn’t find powered external HDDs on a good price when I bought these. My disks were working fine on my plotting machine, it seems that the Pi can’t power that many unpowered disks.
A 3.5 in desktop powered drive is OK with unpowered hubs, but you can use less. I’d recommend no more than a 4 port unpowered hub with 4 powered 3.5 in desktop drives. However, I only recommend powered hubs, and the drive limits are by device + hub not just device or not just hub specifically.