I had the same challenge yesterday @Sergio Suárez
When you start the update process, MacOS will restart, right? But instead booting to the default partition, you will change boot to the additional one that shows. You need to do this couple times during the update process.
I also enabled SIP again on my computer, just in case. But I think this is not mandatory.
Basically, the update is a bootable installer. So, when you change to boot to this additional volume, the update process will start. Apple computers do this automatically, but in our case, we need to choose the boot partition manually.
I hope it helps you ??