My answer is always this:

Blockchain is a structure, called a data structure in programming, no different to a list, array, linked list, all types of data structures you learn about in university but one that was rarely talked about because it had no real use case.

Bitcoin is a set of rules and incentives that uses the Blockchain data structure to provide order, but also uses proof of work and distribution to provide immutability to the Blockchain and also defines monetary policy and needs to constantly be updated to ensure it can work effectively over time just like any software.

The Blockchain is data, it gets appended to, but it doesn't change whollistically like software or a network can, so it is the immutable product of bitcoin.