Update

It should not for now pose a security risk. Eventually when no more security patches are issued for it it may become one if there are vulnerabilities that go un fixed. Currently 12.5.5 is fully updated by Apple.

Good time to start considering a new one, while the older one still works. Start setting asside some money, or trade in the current one for a discount on a new one. See here: link-> Apple Trade In - Apple

If you have iPad Air, iPad mini 2, or iPad mini 3, the latest version of iOS compatible with your device is iOS 12.5.5. This update was released in September 2021 with security fixes for the devices that it can run on. As of right now, I don't think that this is a security risk for your device, considering it was updated relatively recently, but it isn't guaranteed to receive any more updates, so I would consider purchasing another device compatible with the latest versions of iPadOS.

If you're looking for an affordable iPad to replace your current model, I would look at the 10.2-inch iPad (9th generation). Compared to your current device, it is significantly faster and has a larger display, yet is still pretty affordable.

iPad 10.2-inch - Apple

You can also look at other retailers or Apple Certified Refurbished for iPad models that might be less expensive. If you're looking elsewhere, I would keep your eyes out for iPad (6th generation) or newer, or iPad Air (3rd generation), unless you're willing to spend more money.