How can I add my existing home automation to apple homekit without having to scan every item

I have over 100 devices in my home automation... some controlled by individual apps and some other by alexa as well.

However I am interested in adding HomeKit control to simplify the integration of all devices into one single ecosystem with all my other apple devices.

Many devices are installed in the walls, like light switches and dimmers. Others are hidden under furniture like AC swithched outlets or powerstrips, and some others are simply hard to reach.

Is there a way to integrate all without having to expose every device in order to scan it? Can't I just import from the third party apps just as I did with Alexa?