I've got a extension of stay expiring later this month.

 

My options are either a Covid extension or going down the Non-O/ Volunteer visa route.

 

Would prefer to do the Covid extension this time but don't want to close off any future options.

 

Does anyone know if Covid extensions are convertible later or is it a 'waiting to leave' dead-end visa?

 

Appreciate your help!

No, it does not change to original visa type.  You'll still have a valid Non-immigrant visa. 

As Almudena correctly says, so long as you entered the country on a non-O visa, you can continue extend it for various reasons including covid. The original visa remains alive.

 

Like you, I was also concerned that my 60 day covid extension had killed off my non-O, but this is not the case. I just extended again, this time for retirement.