All computers, regardless of manufacturer, eventually become too old to receive system software updates - simply because their internal hardware is not sufficiently powerful or capable of running the latest versions of system software.
App Developers tend to support only the current and previous one or two major versions of the Operating System(s) for which they are Developing and maintaining their Apps. It is simply not economically viable to maintain or update software for devices that are no longer supported by their manufacturer.
Also consider that, for security, Financial and other Institutions often require that customers use computers that are both using a current/supported version of the computer's host Operating System and secure/supported versions of web browser software. Security protocols are frequently updated to protect you from emerging threats. Unless running current/supported software, you be unable to access financial and online services.
If your iPad (or other computer) cannot meet the required minimum requirements, you have no alternative than to replace the computer with a device and OS that does meet the required minima. For iPad, if need to access to Apps requiring the most recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model that supports iPadOS 17/18 - the latter of which will be released later this year.
As such, if your want or need to use Apps that require a more recent version of iPadOS than your iPad is capable, the time will come when you have no alternative other than to replace a device with a much newer or current model.