To add to @JillG's advice, I don't know the layout of your property, is it possible for you to position a Nest Wifi Pro unit closer to your garden but still indoors? That would be the simplest and most pain free way to solve this. As long as the distance isn't too great, it would mesh with your existing Nest Wifi Pro network and extend coverage to your garden.
If that's not feasible, as it mentions in the article linked above, in general, if the extender’s setup instructions don’t make you change Nest Wifi or Google Wifi’s settings, it should work. With that said, there are quite a few things also listed in that article that may not work properly when using a wireless extender. You need to decide if any of those features are important to you.
You want to look for one that has a "repeater" mode and not "AP/router" mode. Repeater mode amplifies and extends your existing Nest Wifi network with the same Wi-Fi network name. Ones that only support AP/router mode, still do that but by creating their own separate Wi-Fi network. Even if you configure it with the same name as your Nest Wifi network, that can cause performance problems.
