How can I install Mac software on my iPad?

you can't by any means

macos apps rely on external libraries which ipadOS lacks

plus only means to install new software of any kind on a non jailbroken iPad or iPhone is apples app store

Some Mac Apps are "universal" - and can be installed on both Mac and iPad. However, the App must be downloaded/installed directly from the Apple App Store.

To be clear, you cannot install Apps for iPad from a ZIP, other archive file or installable media.

LotusPilot wrote:

Some Mac Apps are "universal" - and can be installed on both Mac and iPad. However, the App must be downloaded/installed directly from the Apple App Store.

I don't think the term "Universal" means what you think it does. The original "Universal" applications contained Mac OS X binaries for PowerPC chips and for Intel chips. The current "Universal 2" applications contain macOS binaries for Intel chips and for Apple Silicon chips.

I believe that iPhone and iPad apps must be built for iOS or iPadOS. A developer can't build an app for macOS, and allow (or expect) it to run on an iPhone or iPad. On the other hand, Apple-Silicon-based Macs can run iPhone and iPad apps – if the developers allow it. Presumably macOS includes a complete set of macOS and iOS/iPadOS libraries to permit it to pull off this trick.

Some developers do build versions of their apps for multiple platforms. Examples:

• Safari (Apple)
• Photoshop (Adobe)
• Word (Microsoft)

Servant of Cats wrote:

LotusPilot wrote:

Some Mac Apps are "universal" - and can be installed on both Mac and iPad. However, the App must be downloaded/installed directly from the Apple App Store.

•

I don't think the term "Universal" means what you think it does. The original "Universal" applications contained Mac OS X binaries for PowerPC chips and for Intel chips. The current "Universal 2" applications contain macOS binaries for Intel chips and for Apple Silicon chips.

I am indeed fully aware of the technical aspects.

For the sake of simplicity of explanation, I use "universal" here in the loosest possible sense - hence the quotes.