You could configure the Ipad to act as a mouse with some apps, BUT you wont have pressure support.
Its better to just buy your own drawing tablet. Screenless ones are the cheapest in general, you can find plenty on Amzon on other for around 30-50€ by Huion/XP Pen for an entry level model.
Scrren tablets are much more expensive, an entry model will go for 180-200€.
Screenless tablets are the most basic and the less expensive. They DO require some relearning and adjustments to your hand-eye coordination because with these tablets you are looking at the screen and not your hand (it has its advantages but you need time to adjust to it). For a beginner any model should do, If you want a really good one, the XpPen Deco Pro is great, it basically an Intuos Pro clone with additional features, with tilt support wich is always nice. Its on the pricier side (100€) but you get a solid product.
Screen tablet are more expensive but most people prefer them because they dont like the relearning process that comes with the screenless ones. If you like drawing with your Ipad maybe you should get one, if you have the money for it.
Most tablets should work with Krita (most tablets from Xp pen, Huion and Wacom should work) but in case check this list of known compatible tablets : https://docs.krita.org/en/reference_manual/list_supported_tablets.html