Is scrum only for software projects?

As the Scrum Guide states in the opening section titles "Purpose of the Scrum Guide:

Scrum is a framework for developing, delivering, and sustaining complex products. This Guide contains the definition of Scrum. This definition consists of Scrum’s roles, events, artifacts, and the rules that bind them together. 

The next section starts with a defintion

Scrum (n): A framework within which people can address complex adaptive problems, while productively and creatively delivering products of the highest possible value.

The framework was originally used for software development and a lot of the resources you will find online will speak to the use of it in software development. But it is not exclusively for software development.  I know a Scrum Master that has implemented for us within the People Services (or Human Resources for the old people like me).  I have seen it used in consulting companies where they process large numbers of Requests for Information (RFIs).  I worked for a company where the entire company was using Scrum.  The CEO, CFO, COO, CIO, CTO, etc used it with 1 month Sprints.  The results of their Sprints became the goals of the rest of the organization.  Software Development, Event Management, Sale, Marketing, Client Success all used Scrum in their day to day.  

It can be used for anything where complex adaptive problems are addressed on a frequent, on-going basis.

BTW, here is a link to the Scrum Guide in case you didn't know where to find it.  https://scrumguides.org/  It is free and that is the definitive source for the most recent Scrum Guide.  Any other variation you find on the internet or in print may not be accurate.

Is scrum only for software projects?

It is for any project where the leap-of-faith you can afford to take, before seeing results, is no more than one month long.

In theory, all products and projects except software development are fine.

The key is used properly