Solved: /etc/elogind/logind.conf....

Tried running without jack to test the basic alsa stuff. That works, but only to the internal speakers. Plugging in headphones has no effect - sound still from speakers.
All works fine with an external USB card.

Seems mostly down to jackd1 being installed - removed it, and jackd2 is now running. Still can't get anything out from firefox->pulseaudio...
Had to restart applications as they must have internalised the connections to jack.

I have discovered 'Packages' which does allow me to locate and install packages. I liked Synaptic as it allows you to search for suitable packages in a reasonable manner. Shame that it is not working, and if debian/devuan are moving over to Wayland then it seems it is doomed....

Progress: found references to mediatek chips needing 5.12 kernel, with suggestion to install the xanmod kernel. Managed to do that:

# uname -r
6.1.37-x64v4-xanmod1

I now find wlan0 exists in 'ip address' but NetworkManager, show it with 'not managed'

Deleted the references to wlan0 in /etc/netwprk/interfaces and restarted NetworkManager and wifi has connected!

Thanks for all the help!!

Ahhh, modprobe mt7663 says module not found!

The NetworkManager appears to have the details for my wifi, not sure how, /etc/NetworkManager/system-connections/Wi-Fi\ connection\ 1.nmconnection contains:
-------------------------------------------------------------
[connection]
id=Wi-Fi connection 1
uuid=779db10d-3968-4372-aa75-fa2753fee9f9
type=wifi
permissions=

[wifi]
mac-address-blacklist=
mode=infrastructure
ssid=ChateauPenketh

[wifi-security]
key-mgmt=wpa-psk
psk=??????????            (psk obscured for security, but correct)

[ipv4]
dns-search=
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto

[proxy]

Yes, I did. Now no 'missing firmware' entries on syslog, apart from ones before the reboot.

Extract from lspci -v
-----------------------------------------------------------
0000:02:00.0 Network controller: MEDIATEK Corp. Device 7663
    Subsystem: Lite-On Communications Inc Device 3801
    Flags: fast devsel, IRQ 255, IOMMU group 13
    Memory at 6003000000 (64-bit, prefetchable) [disabled] [size=1M]
    Memory at 6003100000 (64-bit, prefetchable) [disabled] [size=16K]
    Memory at 6003104000 (64-bit, prefetchable) [disabled] [size=4K]
    Capabilities: [80] Express Endpoint, MSI 1f
    Capabilities: [e0] MSI: Enable- Count=1/32 Maskable+ 64bit+
    Capabilities: [f8] Power Management version 3
    Capabilities: [100] Vendor Specific Information: ID=1556 Rev=1 Len=008 <
?>
    Capabilities: [108] Latency Tolerance Reporting
    Capabilities: [110] L1 PM Substates
    Capabilities: [200] Advanced Error Reporting
------------------------------------------------------------------
how do I know if additional firmware is required?