Compatibility
Read the selected mod's release page before downloading. The Minecraft version, mod loader and required dependencies must match your profile. A Fabric build cannot be treated as a Forge build simply because the file is a JAR.
Installation
Back up the world, launch the matching Forge profile once and close the game. Put the compatible mod file in that profile's mods directory, then relaunch. Consult the project's own instructions for any additional configuration.
Adjust Distance
Open the video or mod settings and change one distance setting at a time. Test in a copied world first if you are changing several mods. If the game fails to start, inspect its log and check dependencies before trying a different distance.
Further reading: Minecraft Creator documentation on render and simulation distance. Settings and mod compatibility vary by edition and version.