Using Xarray. Isel to Access Data in Grib2 File from a Specific Location?

I'm trying to access the data in a GRIB2 file at a specific longitude and latitude. I have been following along with this tutorial () approximately 2:52 but my GRIB file is formatted differently to the example and uses different variables

import xarray as xr
import pygrib
ds=xr.open_dataset('testdata.grb2', engine='cfgrib', filter_by_keys={'typeOfLevel': 'heightAboveGround', 'topLevel':2})
ds

This prints:

<xarray.Dataset>
Dimensions:            (latitude: 361, longitude: 720)
Coordinates:
    time               datetime64[ns] ...
    step               timedelta64[ns] ...
    heightAboveGround  float64 ...
  * latitude           (latitude) float64 90.0 89.5 89.0 ... -89.0 -89.5 -90.0
  * longitude          (longitude) float64 0.0 0.5 1.0 1.5 ... 358.5 359.0 359.5
    valid_time         datetime64[ns] ...
Data variables:
    t2m                (latitude, longitude) float32 ...
    sh2                (latitude, longitude) float32 ...
    r2                 (latitude, longitude) float32 ...

I then try to use imshow to index along the latitude and longitude (t2m?) dimension using:

t0_ds = ds.isel(t2m={200,200})

which gives this error:

ValueError: Dimensions {'t2m'} do not exist. Expected one or more of Frozen({'latitude': 361, 'longitude': 720})

Obviously there is an error in the way I'm using isel but I have tried many variations and I can't find much information about this particular error