I am looking for something similar to Transparently Bridge two Networks using MPLS using a hAP ax^3 running 7.13 as the AP and a Raspberry Pi 2 Model B with an Archer T3U USB WiFi adapter running Raspberry Pi OS Lite as the Station.

I only need to attach a single device to the 10/100Mb Ethernet on the Raspberry Pi if that simplifies the problem. The Archer T3U driver supports Access Point (AP) mode. Both eth0 and wlan0 have been configured using NetworkManager (v1.42).

On the Raspberry Pi, something similar to Workaround for a wifi bridge on a Raspberry Pi with proxy arp might be suitable.

However, time has moved on since the two articles were written and they are not directly applicable to the 'WiFi' configuration menu, introduced in RouterOS 7.13 and to Pi OS Lite, based on Debian 12 (bookworm).

Any suggestions or recipes on how to achieve this with current software?

No way.
Or write your driver.