When you go multiarch, you also need to apt-get update and apt-get upgrade; "update" is for updating the local meta files about packages, and "upgrade" is for loading the packages supporting the new architecture.

There's good detail at https://wiki.debian.org/Multiarch/HOWTO

ethtool -P wlan0 might show something, probably the working address though.

mmm then maybe it's the opposite way; that the firmware loads with some random default mac, and this eventually gets updated from the hardware. If so I suppose a binary scan of the firmware could possibly find that first mac...

When you say "no network manager at all" you actually mean "just using ifupdown". That is the traditional network management which is configured by means of a text editor to edit its configuration files... It is indeed the simplest and easiest way with maximal flexibility.

Given that your /etc/resolv.conf is a link it suggests you also have the package resolvconf installed, and that would provide an additional depth to the confusion.

But in any case, DNS setting is part of the DHCP protocol; you know, when your machine contacts the router so as to get an IP address. At that time your machine is also told the IP address of the outbound gateway and the address of the DNS server(s). Those are suggestions by the DHCP server (your router) which get digested by the DHCP client running on your machine. The IP address is assigned to the network interface (via a kernel system call); the gateway IP is assigned to the routing table (via another kernel system call), and the DNS IP address(es) is registered in the file /etc/resolv.conf.

All that happens regardless of which networking software you use; whether it's plain ifupdown, wicd, network-manager or connman.. or whatever.

With resolvconf, you (unbeknowingly?) have opted for a local control of /etc/resolv.conf which is at odds with most networking software unless it also is configured to avoid messing with /etc/resolv.conf. Your first step towards bliss would be to purge resolvconf and reinstate /etc/resolv.conf as a text file.

Yes apt-get update does that. The downloaded "packages" files are kept in /var/lib/apt/lists

It was FUD whether you accept it or not. Sometimes a couple of thoughts before typing can do wonders.

Yes, wicd did/does provide a good and fairly distinct GUI for configuring the network devices and before it was abandoned due to the python2 -> python3 change it was still only in the beginning of its path to enshittification, so quite a good option if one feels a need for a GUI.

The best however is to not use any of those configuration scramblers, but to settle for the original ifupdown system together with wpagui. With those you are seated with maximal flexibility, simple configuration basis by editing text file(s) and a fantastic opportunity catering for any custom networking landscaping.

All it takes is a bit of knowledge which is acquired by means of reading -- reading man pages, starting with man interfaces. Knowledge is power. When you give knowledge away for an idea of convenience, then you lose.

When/if interesting discussions emerge I would be keen to assist with improved platform software.

The programs egrep and fgrep belong to the grep package.
Possibly you have them as /bin/grep and /bin/egrep where they have been residing since yonks. Now everything is supposed to reside in /usr/bin due to a reconfiguration of the root filesystem where all pathnames /bin, /sbin and /lib* are replaced with links to same-named directories under usr.

You may have heard about it as "usrmerge".

Most likely you have updated checking tools that expects/requires those silly-links.

Note that UEFI bios is 32-bit software so booting may have difficulties with an EFI partition beyond 4G byte address. The general advice is always to have that partition first on the disk (i.e. starting at a 1M = 2048 sectors offset).