Im going to a 1x is there a freewheel with more than 34 t on the large gear/cog?
The largest freewheel I found was a 10 speed with 14-36 teeth, or Shimano's &quot;megarange&quot; ones that generally go 14-32 or 14-34.
The rear mech will probably have a model on it.  Searching for &quot;brand model spec&quot; will often give you a manufacturer's specifications page.  To use an arbitrary example, a Shimano Tourney RD-TY300-SGS  google returns https://bike.shimano.com/en-NZ/product/component/tourney/RD-TY300-SGS.html
That page says in part:




Item
Value
Comment




Low sprocket_Max.
34T
The biggest cog should be no-larger than 34 tooth


Low sprocket_Min.
28T
and no smaller than 28 tooth


Max. front difference
20T
Not relevant to a 1x drivetrain


Top sprocket_Max.
14T
The smallest/hardest cog must be 11-14 tooth


Top sprocket_Min.
11T



Total capacity
43T
And this is also irrelevant to a 1x




Aside - your rear derailleur doesn't care if you have a freewheel or a cassette on a freehub.  But it has to match the rear wheel's fitment.
So find your model, search for the specs, and see what its capable of.  You may choose to push the published stats by a little, and probably get away with it.  Something rated 34T will probably be fine at 36T, but 40 would be pushing it.   50 is right out.

Instead of going big at the back, you can also choose a smaller chainring at the front, with the natural consequence of not having a high-enough gear for a big-tailwind or a downhill.
Another option is to have two 1-by chainrings, and use a mechanical system to change from one 1by to the other 1by.  I've heard its possible to have three 1by chainrings on the same bike, potentially giving a sub-1:1 gear ratio at the lowest gearings.
 Seriously though, there's no shame in a double or even a triple chainring if you ride a lot of hills, or even just the occasional steep one.