well, off the top of my head, over the last couple of seasons:
Mikal Bridges
Cam Johnson
Lauri Markkanen
John Collins
Jared Vanderbilt (twice)
Josh Hart
Jermai Grant
Doug McDermott (might not fit the 'young' label)
Rui Hachimura
Jalen McDaniels
now, if you were excluding forwards moved in block-buster trades, that would cut that list down. And if you were talking about all-star level forwards, the list gets even smaller
but forwards do get moved, and many of them are starting level of decent quality
in my view, Portland hasn't had a quality-level pair of starting forwards since Aldridge/Batum. I'm not talking high-quality; just average quality and I don't think Aminu/Harkless met even that average-quality standard, not if consistency was part of the equation. Considering that the power of the NBA is in those 2-way, 6'6-6'10 wings/forwards, the fact that Portland hasn't had a single one in 8 consecutive seasons is management malpractice