Hello! I am a big fan of the Replay Mod, and I would really like a Forge version for 1.17.1. Forge is the environment I am used to and, as a user, the easiest. Although it might be easier to make Fabric mods, it would be really awesome and useful if you would make a 1.17.1 version for Forge. Thanks.

There will not be a Forge port - here is an explanation from the developer (copied from the Discord -> channel "general" in pins)

https://www.reddit.com/r/feedthebeast/comments/c0wkph/modmakers_how_likely_are_you_to_use_fabric_over/er8z4hr/ primarily points 1 & 2 and that I absolutely despise ForgeGradle whereas I haven't yet found any reason to do so with Loom (fabric's equivalent) and for the parts where it's lacking, I've already taken advantage of point 1

You can try the unofficial port from https://github.com/unhappychoice/ReplayMod/releases, but you won't receive support for that version.