Here you can find a list of Forge mods with links to their Fabric alternatives.
The Aether (A Reimagining) (not complete)
BuildCraft (in progress and not publicly available)
Create (in progress)
Galacticraft (in progress)
Mystical Agriculture (stuck in 1.16)
OpenCubicChunks (in progress)
Fabric versions are branches for versions 1.16 and above.
Pixelmon (in progress)
Refined Storage 2 (in progress)
The Twilight Forest (in progress)
YUNG's Better Caves (stuck in 1.16)
RandomPatches (stuck in 1.16)
Tropicraft (stuck in 1.16)
Some other high quality mods made originally for Fabric that you should definitely check out.
Video explaining its features
Architectury is a project which abstracts calls to the Forge and Fabric API allowing mod creators to write a single piece of code for both mod loaders, reducing the amount of code duplicated to support Forge and Fabric.
Patchwork is a project aiming to re-implement the entire Forge API into Fabric, so that any Forge mod jar can simply be patched, and then run as if it were a Fabric mod. Its development is currently on hold.
https://modrinth.com/mod/terralith