Siri does not fully and autonomously control your every facet of Apple devices.
Siri is NOT a robot for your Apple devices
Siri is a simple voice “assistant” to ask questions or information.
It cannot actually act on every piece of information Siri gives you, unlike a real person assistant.
Siri can find information.
Siri can dictate and send a message.
Siri can initiate phone calls from an iPad to an iPhone ( this has to be setup by someone initially )
Siri can initiate FaceTime video calls.
Siri can add reminders and calendar events.
Siri can get you map directions to a location.
Siri can initiate playing music and videos.
Siri can find all of your other Apple devices ( The FindMy app needs to active on all Apple devices )
Tap on these Apple Website links to see what Siri can actually do.
What can I ask Siri? - Official Apple Support
Also, some tasks can be setup, by someone, so Siri is able to initaite some tasks
Shortcuts User Guide - Apple Support
Run shortcuts with Siri, the Shortcuts app, or Siri Suggestions - Apple Support
Of course, all the above needs to be setup by someone.
Someone needs to do actually do all maintenance of an Apple computer or computing device.
It not a the job or design of Siri to do so.
If your iPad needs it data to be backed up, it is up to someone to set this up for your device to backup.
If No access to Mac computer or WindowsPC to do a device data backup using a full computer, you will need to rely on Apple's iCloud to do an iPad backup.
Device backups, to Apple iCloud, can, also, be regularly schedule to take place, so, you do not have to always ask Siri to backup your Apple device.
This means paying a monthly payment to Apple for enough Apple iCloud storage space to allow a full data backup of your iPad using iCloud.
How to back up your iPhone, iPad, and iPod touch - Apple Support
If all of this is beyond your abilities/capabilities to setup on your own, I suggest using the “Get Support” link, at the upper right hand corner of every Apple Support Community Webpage to attempt to schedule an appointment with your nearest Apple Store location.
Apple Store employees will be glad to help/assist you in setting up things on your iPad to make yout iPad do the things you wish it to do, if it can do them
OR seek out a family member who maybe very knowledgeable on Apple mobile devices to help setup your iPad to do some of things you want your iPad to do without you having to initiate the activity yourself.
Best of Luck to You!