I managed to get the SD card reader to work.
H_SDIO_DRV error: sdio card init failed
The WiFi module (ESP32-C6) uses an independent set of dedicated pins (SDIO2_D0 to SDIO2_CK), thus avoiding any physical interface overlap and conflicts.
sd_mmc_card:
id: sd_card
clk_pin: GPIO43
cmd_pin: GPIO44
data0_pin: GPIO39
data1_pin: GPIO40
data2_pin: GPIO41
data3_pin: GPIO42
mode_1bit: false
slot: 0
esp32_hosted:
variant: esp32c6
active_high: true
clk_pin: GPIO12
cmd_pin: GPIO13
d0_pin: GPIO11
d1_pin: GPIO10
d2_pin: GPIO9
d3_pin: GPIO8
reset_pin: GPIO15
slot: 1