This is not exactly what you are looking for but is what I have in both my garage and back yard.
https://www.crutchfield.com/p_022WXA50DS/Yamaha-WXA-50.html?tp=63339&awkw=199636298425&awat=pla&awnw=g&awcr=102161561185&awdv=c&awug=9031857&gclid=EAIaIQobChMI75Pm2K7-3AIVUm1-Ch03AgZPEAQYEiABEgIBAfD_BwE
It's a small receiver/amplifier that can receive either blue tooth or wi-fi and then you connect to the speakers of your choice. I went this route since most wireless speakers need to be plugged into a power source which are rarely in the place you want your speakers.
In my case, I mounted my speakers from the ceiling and then routed the speaker wire to the receiver - just like a home stereo but this thing is about the size of a car stereo and puts out plenty of power. It is connected to my home wi-fi (as is my main stereo & backyard unit) and then you can use the Yahama app to sink all three (or use separate). Perfect for partys or just working in the garage. It's not cheap but not outreagous.
My backyard unit is currently not permanently plugged in until I find/create a suitable location. Instead, I have my speakers permanently installed and wires routed to where I use this stereo. When I have party's, I hook I it up for use. My plan is to build a waterproof containment spot and then leave it out year round. My yard does not have a patio cover so I don't leave this out in the open.