@jonl1969 

I'd suggest running a ethernet down to your garden room and getting a extender or another router that can have AP mode. 

I've got a mancave at the bottom of my garden and was having similar issues, 

I ended up buying another Ax72 and putting it in AP mode using same ssid password ect as my main router Software when I move between my main and go into my mancave my phone switches over to that unit and vise versa when I go back in doors 

  @Basboi85 Many thanks for the help. I was trying to avoid a cable, but coming round to the idea now. thanks 

  @terziyski many thanks for the reply. I was trying to avoid a cable but coming round to the idea now, as I do have a decent route to get one there without much hassle. thanks

  @Joseph-TP thanks for the reply. I have a garden "room" in my garden (a large shed basically) so its inside that that Im looking for good wifi. Outside is already good. thanks.

  @jonl1969 

I personally from my experience  would advise as you said you have power in your 'shed' would be if you can run a ethernet from your main router (out door rated 5e or above) and then attach it to a extender or router then run it in AP mode. 

In my set up i have a AX72 in AP mode down in my mancave/outbuilding( about 30m) connected via ethernet to my main AX72 inside of my house which gives me full wifi speeds as well as full ethernet speeds plus I have 4 extra ethernet ports that utilise 2 for my tapo cameras. 

When I'm inside my mancave I get full speeds ect it's only when I go outside into my garden that I get a speed drop as of the wood and insulation affects it but I have more than enough speed/signal coverage in my garden and then drops off by the time I go into my house then my phone switches over to the main unit wifi. 

Depending on your budget and sometimes you can pick up wifi6 routers cheaper than the extenders 

  @Basboi85 thanks for the extra info. Not easy to get to my router as this is in a front bedroom upstairs. Would you agree that I could (as far easier & as another contributor has said) take an ethernet cable from an extender im already using at the rear of the house (in living room) up to the shed & buy another extender (in AP mode) & use that. Guessing coming from the router is best, but extender to extender (in AP mode) would work too ? not doubting what others have kindly said, but thought id get your take on that too, as youve only mentioned router to router (in AP mode) thanks 

  @jonl1969 

I personally couldn't comment or advise on extender to extender as I've not owned/used or set up one but im just offering my experience where i have 3xAX72's in my property and i have 2 in AP mode.

i dont see why it wouldnt work if it supports easymesh then I see no issue in doing so I'm just a big advocate of hard wiring between units and I think you would get far better wifi signal/speed from a router then a extender on the views of most routers have multiple larger antenna. 

From my understanding if you was to do easymesh via wifi is that in theory it should work, 

My only 2 pence worth on wifi easy mesh  although it can help and be a god send in many cases where not being able to run wires is easy or able to be done it does come in my personal opinion with a big drawback and that the end device connected via wireless easymesh is at the mercy of the signal it receives and depending where you can place the unit due to power outlets. 

Ie in your case, 

You get  hypothetically 100 down/  20 up from the isp

 Your extender in your living room is hard wired via ethernet to your router and receives the full speeds, 

Depending on how much signal (wirelessly ) you new extender would get in your mancave/shed  due to distance and interference from neighbouring signals can impact the speed you get from your now repeater hypothetically only able to give you a minimal amount. 

Hypothetically speaking if you daisy chain via wifi easymesh from router)))((( extender)))((()))((new extender you could have lost upto 75% of you isp max speed by the time you factor in how much you've lost from router to 1st ext then wirelessly again to new extender due to factors of where you live and how your building materials are. 

You can download apps which I strongly advise before you buy anything as this will give you more solid info on what potentially be best for your scenario. 

wifi man in my opinion is the easiest in terms of layout and using it as its shows you in real time you wifi signal strength as you move away from your router to your extender ( when you move between access points) , it shows you wifi channels as well as neighbouring signals ect.  It can also measure your signal quality and also shows you neigbouring signals strengths aswell so you could test how much potential signal quality you would lose from walking away from your living room extender down to the bottom of your garden and going into your mancave/shed. 

I'm not way a pro or anything just a newbie and just thought I would share how I've done mine and it just gives you options to help make a choice that will be best for you as in the long run save you money 

Bit of a long winded reply so my apologies