Note: If you have Optifine installed, then there are some options that you most likely will need to disable in Optifine, or otherwise it will break the schematic rendering: If you are for example on AZERTY keyboard layout instead, then the keys are different, and M + C becomes, + C instead, etc. The default hotkey to open the in-game config GUI is M + C. Litematica was started as an alternative for Schematica, for players who don’t want to have Forge installed on their client, and that’s why it was developed for Liteloader.
There are also Forge versions for 1.12.2, and Forge ports for 1.14.4+ are also planned, but Forge will need to start shipping the Mixin library before those can happen. It has also been ported to Rift on MC 1.13.2, and for Fabric on MC 1.14 and later. It’s primarily developed on MC 1.12.2 for LiteLoader. Litematica Mod (1.19.1, 1.18.2) is a client-side schematic mod for Minecraft, with also lots of extra functionality especially for creative mode (such as schematic pasting, area cloning, moving, filling, deletion).
