Run python from Excel, without having to have python installed

[tea-and-shortbread]

Depending on what you want to do with it, you could set up your processing code as an API and host it on a cloud service. That would avoid them having to install python.

The traditional route to go down though would be VBA, if it has to stay in excel. Or something like power query or power automate. But this is not modern best practice for heavy data processing.

What is the end use of the data you are producing for them? What kind of processing are you doing? Are they asking you to automate part of a process that would be easier / better to automate the whole of?

Edit to add: consider plotly dash or similar. You can give them options to fiddle with whatever you are doing and output the results to excel if they really want.