Thank you both for your help. I have now tested with the 12.90 version and got the AX210 card to work. The required drivers are as per HiassofT's post, although lower versions are supported as well:
LibreELEC (chewitt): 12.90.1 (RPi5.aarch64)
LibreELEC:~ # dmesg | grep iwlwifi
[ 2.628284] iwlwifi 0001:01:00.0: enabling device (0000 -> 0002)
[ 2.662563] iwlwifi 0001:01:00.0: Detected crf-id 0x400410, cnv-id 0x400410 wfpm id 0x80000000
[ 2.662584] iwlwifi 0001:01:00.0: PCI dev 2725/0024, rev=0x420, rfid=0x10d000
[ 2.662590] iwlwifi 0001:01:00.0: Detected Intel(R) Wi-Fi 6 AX210 160MHz
[ 2.662996] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-89.ucode failed with error -2
[ 2.663019] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-88.ucode failed with error -2
[ 2.663029] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-87.ucode failed with error -2
[ 2.663046] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-86.ucode failed with error -2
[ 2.663056] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-85.ucode failed with error -2
[ 2.663066] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-84.ucode failed with error -2
[ 2.663075] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-83.ucode failed with error -2
[ 2.663085] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-82.ucode failed with error -2
[ 2.663095] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-81.ucode failed with error -2
[ 2.663104] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-80.ucode failed with error -2
[ 2.663113] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-79.ucode failed with error -2
[ 2.663124] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-78.ucode failed with error -2
[ 2.663133] iwlwifi 0001:01:00.0: Direct firmware load for iwlwifi-ty-a0-gf-a0-77.ucode failed with error -2
[ 2.663136] iwlwifi 0001:01:00.0: no suitable firmware found!
[ 2.663138] iwlwifi 0001:01:00.0: minimum version required: iwlwifi-ty-a0-gf-a0-77
[ 2.663140] iwlwifi 0001:01:00.0: maximum version supported: iwlwifi-ty-a0-gf-a0-89
[ 2.663142] iwlwifi 0001:01:00.0: check git://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git
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The key to getting it to work was to use the firmware from the /plain directory, not the /tree directory, so these two files:
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/intel/iwlwifi/iwlwifi-ty-a0-gf-a0-89.ucode
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/intel/iwlwifi/iwlwifi-ty-a0-gf-a0.pnvm
After downloading them into the /storage/.config/firmware directory, the firmware is found and installed. If you use the files from the /tree directory it produces a "uCode file size ... does not match expected size" error.
Output with firmware correctly installed and wlan1 configured:
LibreELEC (chewitt): 12.90.1 (RPi5.aarch64)
LibreELEC:~ # dmesg | iwgrep iwlwifi
[ 2.990156] iwlwifi 0001:01:00.0: enabling device (0000 -> 0002)
[ 3.002776] iwlwifi 0001:01:00.0: Detected crf-id 0x400410, cnv-id 0x400410 wfpm id 0x80000000
[ 3.002822] iwlwifi 0001:01:00.0: PCI dev 2725/0024, rev=0x420, rfid=0x10d000
[ 3.002837] iwlwifi 0001:01:00.0: Detected Intel(R) Wi-Fi 6 AX210 160MHz
[ 3.032280] iwlwifi 0001:01:00.0: capa flags index 4 larger than supported by driver
[ 3.032296] iwlwifi 0001:01:00.0: TLV_FW_FSEQ_VERSION: FSEQ Version: 0.0.2.42
[ 3.033324] iwlwifi 0001:01:00.0: loaded firmware version 89.7207fc64.0 ty-a0-gf-a0-89.ucode op_mode iwlmvm
[ 3.513936] iwlwifi 0001:01:00.0: WFPM_UMAC_PD_NOTIFICATION: 0x20
[ 3.513963] iwlwifi 0001:01:00.0: WFPM_LMAC2_PD_NOTIFICATION: 0x1f
[ 3.513973] iwlwifi 0001:01:00.0: WFPM_AUTH_KEY_0: 0x90
[ 3.513982] iwlwifi 0001:01:00.0: CNVI_SCU_SEQ_DATA_DW9: 0x0
[ 3.514025] iwlwifi 0001:01:00.0: Detected RF GF, rfid=0x10d000
[ 3.516596] iwlwifi 0001:01:00.0: loaded PNVM version 285b3568
[ 3.600176] iwlwifi 0001:01:00.0: base HW address: 70:15:fb:10:b1:1b
[ 3.898834] iwlwifi 0001:01:00.0: WFPM_UMAC_PD_NOTIFICATION: 0x20
[ 3.898856] iwlwifi 0001:01:00.0: WFPM_LMAC2_PD_NOTIFICATION: 0x1f
[ 3.898867] iwlwifi 0001:01:00.0: WFPM_AUTH_KEY_0: 0x90
[ 3.898876] iwlwifi 0001:01:00.0: CNVI_SCU_SEQ_DATA_DW9: 0x0
LibreELEC:~ # ifconfirg -qa
eth0 Link encap:Ethernet HWaddr 2C:CF:67:2C:88:8C
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:110
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:37 errors:0 dropped:0 overruns:0 frame:0
TX packets:37 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:12744 (12.4 KiB) TX bytes:12744 (12.4 KiB)
wlan0 Link encap:Ethernet HWaddr 2C:CF:67:2C:88:8D
inet addr:192.168.1.213 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:162 errors:0 dropped:0 overruns:0 frame:0
TX packets:162 errors:0 dropped:1 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:25801 (25.1 KiB) TX bytes:38627 (37.7 KiB)
wlan1 Link encap:Ethernet HWaddr 70:15:FB:10:B1:1B
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
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I will test with the 12.2 nightly build later today and report back.