MacOS keeps asking me about setting up an iCloud account but most software works without it. Tweetbot for example needs an iCloud account for syncing between devices. When you buy software via the Apple App Store of course you'll need an Apple Id. Security updates and can be installed without one. I switched off all telemetry and for a while had a software to track network connections (https://www.obdev.at/products/littlesnitch/index.html) installed. Connections to Apple were all explainable, e.g. to sync the time (can be switch off).