I use Behr Premium Transparent Waterproofing Wood Stain, Clear No. 500N. I have it on fir siding, T11 pine siding, pressed board siding, , and 1x6 x 6 ft high cedar fencing. It has some pigment in it that does give the wood some color.
It last about 4-5 years until it needs redone. On oak though I am not sure how any stain/ waterproofing will work well due to the grain structure when compared to a softer wood. It will not soak in as readily. Previously I used boiled linseed oil sprayed on with a high pressure paint sprayer, but that takes a long time to dry if it ever does.
The more pigment in the stain, the better UV protection you will get
