As a simpler, cheaper example of off-grid with grid assist I use an MPP Solar 3048LV AIO in my camp trailer. You feed it 120v AC input, PV input, and 48v battery input. It provides up to 3000w of 120v AC output. Here's a link -
https://shopsolarkits.com/products/...-145vdc-battery-charger-60a-3048lv-mk-3kw-48v
I'm not pushing MPP Solar but just providing an example. If you go to youtube and see one of these off-grid AIO's installed, hooked up, you'll see the 120v AC, PV, and battery connections and it might make sense for you.
@Will Prowse has done a TON of great youtubes on various AIOs (MPP Solar, EG4, Growatt, xxxx, and high end Victron etc) would be a suggestion to get started.
Here's a basic AIO off-grid w/grid assist.
At the next level from 120v only is US 240v/120v split-phase. This is the same in concept but you need a more expensive unit or to parallel 2 x 120v units to get the 240v. Unless you need 240v I might suggest just something smaller/cheaper and just get it working.... and gain a TON of experience, 1st runs of wire, and upgrade from there. Once you have a basic system and operate it, things will start to become clear and help you with more advanced growth assuming you DIY!!
If not DIY and $ are not a big issue, then they're making pretty beefy 'power stations' these days and they even have wheels - you can just roll it into the garage and hook it up to a critical loads panel. Starting at 8:50 in this youtube you can see a DIY install of one of these units but an electrician can do the install part for you.