If you are looking to install Logic Pro X 10.3.3 safely and legally, here is a guide on how to manage this specific version. Official Acquisition and Compatibility Logic Pro X 10.3.3 was released in late 2017. It is the final version compatible with macOS 10.11 El Capitan Apple Discussions

: Version 10.3 featured a modern, brighter interface designed for better legibility in various lighting.

If you’d like, I can instead help with any of the following legal and useful alternatives:

Improved high-definition mode for the and Amp Designer plugins, offering up to 12x performance gains.

Older versions like 10.3.3 are useful for legacy Intel Macs that cannot run newer macOS versions. 3. Risks of "TNT" DMG Files