There's https://shota.house which is a loli/shota safe twitter-like platform that @burger@Burger@burggit.moe and myself run. Here's an invite link: https://shota.house/registration/EdCGgm8zBpFuMFKpVrCvOZOP5VKvEwDCGLyJr_M4rZY= just sign up and log in. (Good for multiple people, if other Burggit users want to join)

There's also baraag.net which is a very large art posting instance (also twitter-like) for loli/shota enjoyers.

There's https://gelbooru.com/ which is an art posting gallery where you can find various anime images, including loli/shota (but has to be enabled in settings)

there's https://allthefallen.moe/ which runs various loli/shota focused sites/services.

that's basically all I know of at the moment.