1. Farsight have already done Operation Highjump: ETs, not the Germans had the advanced aircrafts which forced Byrd to leave. (According to Farsight)
2. The Germans had very advanced technology, but not as advanced as the UFO technology. They had A-Bombs and would have dropped them on London, the Cremlin and the White House if they would have had the means to do so. But they did not use these, because it made no sense to use these on European soil at the end of the war. Just a few UFO type aircraft would have been enough to get air superiority over Europe and this was the weakest point for the Germans. They would have been concentrating on these, but they focused on Me 262 mass production -why? There may have been some prototypes of disc shaped aircraft at the end of the war, but with conventional drive. And after the war they may have had some places in South America, Syria, Asia, etc. to hide and produce ("normal") weapons in a small scale. But nothing in comparison to the huge resources they had in Germany and Austria: Unlimited funding, millions of forced workers, a huge industry, highly skilled workforce and many of the best scientists have not been able to achieve it and then some exile scientists and their small staff in Argentina, Chile, the Amazon djungle or in antarctica did it within a single year? -Makes no sense at all. Maybe later, with the help of the NASA/US/CIA deepstate, but not as early as in 1946/47.

I think most of us are familiar with the material from Farsight. But I would also remain a bit skeptical of their RV material, because we don't really know the true intentions of the ETs behind them. Farsight believes that ETs helped the Germans during High Jump, but we don't really know how early and how far the Germans had been involved with UFO tech and aliens. Courtney doesn't necessarily release all the RV data. You won't see things that don't fit his narrative.

Also, it could well be that the knowledge of the UFO/ET stuff was only open to a small select group within the German/Nazi military, and maybe they didn't necessarily intend to use that technology during the war, because maybe they realized the enormous potential that they had in their hands, that suddenly the entire galaxy had opened up to them, so better keep silent and hidden, develop outside of earth and control things here from a distance, instead of wasting resources fighting a pointless war.

Check out the Buzz Aldrin RV project at FFG. They found indications that the Germans had already been there in the region where the portal is.