There’s nothing “random” about it.

Microsoft releases their updates (except really time critical security updates) during Patch Tuesday, the second Tuesday of each month.

You can delay restarting after updates do the initial install, which it does in the background after downloading by default, for 7 days before it starts pushing you. The restart is needed when files that are currently in use need updating, not all updates require that.

At any point you can also schedule an update time for it to finish the install. And you can set active hours for it to not update during times when you usually use your system.

If you continue to ignore finishing the update process, it will eventually consider it critical (after like a month of delayed updates) and will force an update on its own because you’ve been delaying it for so long, you are not attempting to schedule it, and you are not telling the system to pause updates. So you’re literally ignoring every option given to you to manage updates.

Your system “randomly” updating means you are not utilizing the options to schedule and plan times the system can regularly update, AND are not keeping your system anywhere near up to date manually.