If Radeon GPUs have a Shader Cache option that can be enabled/disabled for a specific program that overrides the global setting, then try disabling it just for Destiny 2 specifically. I don't know if it would work for a Radeon, but I've been having similar issues with a 2060, and I tried turning off the Shader Cache setting just for Destiny 2 from the GPU's control center, and it made the biggest of differences for me, everything was running smoothly again (but I believe it's because something in the game's code mucked up how Shader Cache works for that game, making it so instead of helping improve performance, shader cache only worsens it).