Well this is a frustrating problem. If you are trying to use Hue, then you will find that it needs to have a light bulb pretty close to it. That is because it using mesh networking over 2.4GHz with Zigbee.
The solutions are pretty uninspiring. Basically, you need to put another bulb between the hub and the bulb that can’t connect. This is going to be pretty hard if it is a detached garage or something.
If you have ethernet out there, you could put another Philips hub out there, but then you are in effect running two houses which is pretty inconvenient.
The other solution is to get a Wifi light bulb and get an access point out there. So go non-Hue and just get a Wifi bulb like the Vocolinc which works pretty well
Notes on managing multiple HomeKit Vendors you need their native apps
As an aside, why does every one of these vendors have to have their own control system that gloms every other Homekit device, it is just super confusing. Homekit for example can’t delete devices, you have to do that in the native application, so if you want to remove a Philips Hue bulb, you need to reload that application.
Why we need to wait for Thread rather than use Wifi and Bluetooth.
The power consumption requirements is the main thing. For instance, if you want a simple “contact sensor” that tells you if a door is open, with a conventional alarm system, it can be five years before you need to replace the battery, but with Bluetooth 5.0, the batteries last six months. That is a lot of battery changing! So the newest technology is Thread which Apple is backing. Zigbee as noted above is used by Hue and has a 35 foot range, but thread is 100 feet. There is also Z-wave out there, but it is not an open standard. The nicest thing is that Thread is at 2.4GHz so it will work worldwide and is IP based and open.