Can I update my iPad mini 4 to iOS 17?

No and never.

A 2015 iPad Mini 4 is forever locked to some version of iPadOS 15, currently at iPadOS 15.8, now/apparently.

Many third party apps still support iPadOS 15 as a minimum OS requirement and will continue to do so for a another year, or so.

If you have third party apps that need a higher iPadOS version, then you will need to purchase a new or “newer” ( refurhished or used, secondhand ) iPad model.

There are PLENTY of newer, older iPad models that can run the latest, current versions of iPadOS.

If you need OR ONLY able to afford to purchase older, less expensive iPad models, look at older IPads from 2017 and later.

All of these older model iPads below CAN, currently, run the latest releases of iPadOS 17.

2017, 12.9 inch screen iPad Pro models ( 1st gen Pencil support )

2017, 10.5 inch screen iPad Pro models ( 1st gen Pencil support )

( The above iPad models, probably, are at their last full year of full Apple OS support. )

2018 11 inch or 12.9 inch screen iPad Pro models ( 2nd gen Pencil support )

2020 11 inch or 12.9 inch screen iPad Pro models ( 2nd gen Pencil support )

2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )

2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )

2020, 10.2 inch screen iPad 8th gen models ( 1st gen Pencil support )

2020, 10.2 inch screen iPad 8th gen models ( 1st gen Pencil support )

2021, 10.2 inch screen iPad 9th gen models ( 1st gen Pencil support )

2018, 11 inch or 12.9 inch screen iPad Pro models ( 2nd gen Pencil support )

2019, 10.5 inch screen iPad Air 3rd gen models ( 1st gen Pencil support )

2021 10.9 inch screen iPad Air 4th gen models ( 2nd gen Pencil support )

2019, 7.9 inch screen iPad Mini 5th gen models ( 1st gen Pencil support )

2021 8.3 inch screen iPad Mini 6th gen models ( 2nd gen Pencil support )

Get the largest internal data storage model you can afford as NO Apple iOS device has ANY expandable storage.

forever.

Best of Luck to You!

No. See this list for compatible devices.

iPad models compatible with iPadOS 17 - Apple Support

If you decide to go down the path of purchasing used, secondhand Apple devices, from individual Apple device sellers, here is how to avoid purchasing an Apple iOS/iPadOS device with user activation lock, in the future.

If you purchase any iPad, or any Apple iOS device, for that matter, used/second hand, online, or even in-person, make sure this iPad does NOT have user activation lock and has been properly reset for sale.

A properly reset for sale iPad should initially power up to an animated, multi-language “Welcome” screen.

DO NOT take the iPad seller's word that this iPad is user activation lock free!

We have seen plenty of used iOS device purchasers get scammed.

User Activation Lock can never be bypasss, circumvented or worked around IF there is no correct previous/original user information to be able to do so.

Apple doesn't get involved with ANY user activation locked, used/second-hand sold devices, either.

So, buyer beware!

If purchasing a used device in-person, power the iPad ON

If the iPad DOES NOT display the initial animated, multi-language “Welcome” screen, then pass on purchasing this iPad.

If the iPad powers up to any other screen, then forget purchasing this iPad.

You cannot trust that the seller actually has the correct needed info to properly reset the iPad back to factory settings right then and there before the actual purchase and exchange of money for the iPad, in question.

Pass on the device!

If you are purchasing this used iPad online ask the seller to provide multiple images, either online or be sent to you via email, showing this animated, multi-language “Welcome” screen of the interested in purchasing iPad model.

Even better, ask for a short video be sent to you showing this animated, multi-language “Welcome” screen, in action and in its entirety, posted to the online ad or emailed to you.

If the online iPad seller refuses any of these requests, pass on the iPad. DO NOT buy!

Good Luck to You!