This is a deliberate design choice by Autodesk to encourage upgrades. When a file is saved in a newer version, it may contain scene data, modifiers, or render elements that simply don't exist in the older code base.
Several online tools offer 3ds Max file conversion to older versions. These tools allow you to upload your file, select the target version, and download the converted file. Here are some popular options: Convert 3ds Max File To Older Version Online
Convert 3ds Max Files to Older Versions Online: The Ultimate Guide This is a deliberate design choice by Autodesk
Converting a 3ds Max file to an older version online is not a standard native feature, as the .max format is typically proprietary and strictly versioned. However, you can achieve this through official software methods, third-party online converters, or universal file formats. These tools allow you to upload your file,
If you used a modifier introduced in 3ds Max 2024, it will be deleted or collapsed when saved back to 2021.