I believe it's been a collaboration "with" Palmer, whether it still is now hasn't been specifically stated. As reported in this interesting article from Jan 2022: https://www.sportsbusinessjournal.com/Daily/Issues/2022/01/24/Technology/josh-allen-embraces-technology-to-transform-himself-from-loose-cannon-to-maybe-a-3d-mvp.aspx
"private sessions with quarterback whisperer Jordan Palmer, who, in March of 2020, introduced Allen to a football-technology whisperer: Chris Hess"
"His prime advice was for Allen to work with Palmer on not lifting his back heel before planting his front stride foot, essentially to create proper ground force."
And this from May 8, 2024 https://buffalowdown.com/posts/mechanics-source-bills-josh-allen-rise-2020-01hvt06fdyn1 implies he still is working with Palmer. "Since the pre-draft process and during the offseason, Allen has worked with Palmer to improve his arm mechanics, footwork, and game knowledge. The specific change Palmer is widely known to have influenced Allen is his arm mechanics."
From another old article: Josh Allen works with Palmer (left) and Mike White (far right), a biomechanics specialist who helps Palmer's clients to refine their throwing motions.