What is the advantage,if any, of blend engine oils over fully synthetic such as Motocraft Blend oil ?

Nothing. Price, maybe?

hard to even find conventional only and the price is hardly if any less, nearly everything is a blend or full synth

I suppose it helps them meet the certification ratings

or they make so much synthetic that the lower grade synth is worth calling a blend and putting in bottles

No additional benefit to synthetic blend. Spend the extra $10 on synthetic oil and synthetic filter a run it 3 times as long as conventional oil.

Run a blend in my 2019 but was what was in it synthetic isn’t much more dollars

The problem with blends is there isnt a minimun amount of each oils in the blend required by law. So if I take .99 wuarts of conventional oil and add .01 quart of synthetic it is considered a blend the same as a 50 50 conventional to synthetic oil blend is. Its smoke and mirrors advertising.

yup
all advertising is false advertising , it's just who is selling the smallest lie.

which is why there are 50+ quarts of different blend and 50+ quarts of different synthetic filling the wall at Fleet Farm and 5 little spots for conventional in 5w30 5w20 10w30 10w40 and 30w

and the conventional is the same price as many of the blends

they market it different and jack all the prices up.