Understanding CSM support for HBAs etc

Hi,

I am building an unraid setup using z690 board. I want to install more than 20 hdds and using the onboard SATAs are great but will also need a HBA.

I was to use an LSI 20 port PCIE x8 HBA to go with the mobo, something like a 9300-16i in IT mode.

From what I can see with the board I will need to enable CSM compatibility mode so that I can use this expansion card. I'm using an iGPU via the intel i3 CPU.

I only have:
1 x16 slot
1 x4 slot
2 x1 slots

I really need the x16 slot for the HBA but can install another GPU in the x1 slot.

Does anyone know if using the x1 slot for GPU and then placing the LSI HBA will first solve the CSM compatibility issue to see LSI HBA sata cards but also enable me to troubleshoot with an x1 pcie GPU?

Thanks