You could try Artemis Dehalo (or Artemis Strong Dehalo) Proteus also has a Dehalo slider. The idea of “Dehalo” is meant for unsharpening oversharped video. If this doesn’t work, then you may have to blur the video using a separate program.
Proteus is probably the best bet, The “Revert Compression” Slider will smooth out alot of Artifacts and Dehalo will soften all the dark lines at the expense of blurring the image if used too much. Dione models are the best IMO but bad compression or other digital junk gets heavily exaggerated with Dione. Dione Interlaced Robust Dehalo generally works well for a non intrusive dehalo, but it has problems with digital junk and can look horrible.
I sometimes run a dione model at say 200%, then run it again at 100% with Proteus with the Revert Compression slider almost all the way up