The latest plugs and switches I bought were
They normally use a cloud based system called and controlled through an app called smartlife. But you can flash them "over the air" using a computer and a cell. Look up "tuya convert"
Manufacturers are waking up and making it harder to do that by updating the firmware process (it's a hole in the current update process that allows to install another firmware) or changing the hardware to make it incompatible with Tasmota.
Another option is to use Sonoff devices, which was the intended target for Tasmota but they are more cumbersome to use IMHO.
Home Assistant can run on a Raspberry Pi 3b and 4. They cost around $100 for a system with SD card, power supply and case. You simply install Home Assistant on the SD card and put it in the Raspberry Pi. Nothing more to it to install. Then it's the configuration that will take the most time. Their community forum and discord channel are very active and usually get an answer the same day if not hour.
Home Assistant can support Zigbee and Z-Wave devices as well as over 100 different integrations. My latest integration is speedtest.net in my Home Assistant at the cottage. When I'm not there, it will test the Internet speed once per hour and report its speed in a graph. I want to document my DSL internet speed so I can open an incident with them if it's not what I pay for.