SATA-Port not working on Asus Mainboard

I have a Asus Prime Z370-A Mainboard.

• 6 SATA ports: 5 SATA drives plugged on ports 2 - 5
• 2 M2 ports: 1 SSD installed on port 1 with Auto-Detection. The empty port is set to "half speed" X2 mode

The M2 SSD (SATA) on M2-Port No.1 has been installed recently. This disables SATA-Port No. 1 according to the manual of the Motherboard. Problem is that SATA port 2 also doesn't work anymore. This should not happen to my unterstanding of the manual.

I have a W11/Fedora dual boot system. Secure boot and TPM enabled.

Is there any setting that could prevent the motherboard from recognizing drives on port 2? Is it wise to deactivate AHCI?

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