My electric lawn mower won't start after getting grass blocking the blade
I've cut through meter-high grasses and other stuff with a plain lawnmower.  The trick is, you need to go very, very, very slowly.  And listen closely to the machine, it will make detectable noises when it is starting to overload and you must detect and respond swiftly to stop that.
Also, this is a time you'll want those blades super sharp.  So if you have the means, keep em bright!
It's gonna take an age, compared to what you're used to.  You won't like that.  But don't think about how miserable the job is today, think of the dozen times this year you didn't have to do it.  It's a huge net savings, so you should be happy.