There's a project called "Stop Mod Reposts" which maintains a list of sites known to re-distribute content without permission, either for advertisement revenue or for malware reasons. You can find that project here which includes a browser extension to alert you to known problem websites. You can find a full list of known problem websites in their GitHub repository: https://github.com/StopModReposts/Illegal-Mod-Sites/blob/master/SITES.md
Note that this list includes minecraft-downloads com so we can be confident that the website is not real.
The only form of modding closest to Forge for 1.13 is Rift Modloader (which is a placeholder modloader until Forge for 1.13 in my eyes, I have used it many times and know a lot about it learning what works, what is new, whats a Rift ported mod and I know many mods are supporting over time like how mods support Liteloader besides Forge, so I know its legit mod files or a legit modloader or else I wouldn't be stating it, but there is no legit Forge for 1.13 yet to the public for players to download. If there were people would know about it and Twitch would support it, which since it doesn't exist as of yet, its not a thing and only is for dodgey sites to state false things).
I am also documenting Rift mods I know are supported by Rift that appear on the Curseforge site only so I know what is legit or not, I update this thread often on these Forums so I stay with the Curse sites for safety and legit sources of mod files and the Rift modloader files and know I'm giving good information to players that is safe on the same sites and are monitored very well so I can't hopefully get the information wrong. The only other time I would state if a mod isn't on Curse is github (like with Aether Legacy Rift Edition or Rift releases not on Curse for reasons I want to know), but I put 90% of the mods listed that are 1.13 Rift Modloader supported towards Curse only. My proof of my thread and what Rift is about.
And the closest to content other than Rift mods is Datapacks. So only 1.13 Rift mods and Datapacks are the only community content of note to me that act like mods. And I've used many and their monitored and safe on Curse Sites, so you know its ok to use them unlike say Planet Minecraft (for datapacks) that the downloads aren't always great or redirecting to unsafe places so I try to avoid that source as much as possible and stick with Curseforge or other Curse sites instead.
The legal site for Rift is Curseforge, which Curseforge is obviously a safe website source like the other Curse sites like the Forums here :). But otherwise yes, Forge's major website is those listed above and the others are dodgey.