It was there before around Forge 1.13.2 version 44 or so last I checked, I have no clue why it's gone. It didn't work properly anyways when it was visible so I assume their working on something.
I wish they would allow Rift to work since Rift works fine enough for it's mods and Forge 1.13.2 & Rift mods appearing is a mess, unlike Liteloader having it's own place and Fabric having it's own category on curseforge but is for 1.14 snapshots instead of 1.13 versions of the game, Rift just gets left alone but works fine-ish for 1.13 and 1.13.2 depending on the mods you use, small ones works fine, Aether Legacy not so much, most work fine enough from my time with them and still with it but it's been a while since I last touched Rift since I focus on Fabric so much.
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But on the Forge side of things, to be on topic; it isn't ready yet even for being a public beta period. Most mods are ports being worked out to 'adjust' to 1.13.2 Forge anyways so they are far from ready either. Wait a bit or test mods/Forge 1.13.2 out on Vanilla for now but Twitch and MultiMC are waiting it out for now until it's out of public beta and more ready.
Unlike say other public Forge betas for 1.10 for example which are bad for stability but not as bad as maybe 1.13.2 Forge where it's able to work but it's recommended for users yet to move forward and play like 1.12.2 is still to recommend. As some one testing them (not reporting though since I focus to much on Rift & Fabric modloader environments mostly) but it's not stable enough yet Forge for 1.13.2 to use, not bad on crashes unstable but just not ready to call it modpacks posting or use mods in a survival ready.
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Niche Mod Finder/Acknowledger/Tester/Player. Fan of Datapacks, Rift 1.13/1.13.2 Mods, Fabric 1.14 Mods and interesting underrated or new 1.12.2 and below versions of mods. :) Testing 1.13.2 Forge and Fabric 1.14 mods mostly though.
I sometimes create the odd modpack or adventure map once an idea comes together.