Apple doesn't pre-announce end-of-support dates. That said, history demonstrates that iPad models typically receive five to seven years of hardware and OS-update support from initial release of a device model. In the latter period of support, update support becomes limited to occasional security updates.
While older devices continue to have utility beyond the mainstream period of support, they will inevitably become more prone to unpatched and emerging security threats and exploits. Be aware that some websites and online services require devices to be using a fully supported OS/browser versions, in particular financial and banking services that sometimes only support the current and prior one or two major OS versions.
Your second generation iPad Pro (released June 2017) is certainly within its twilight - and for this reason, if using your iPad for sensitive or financial purposes, you might be well advised to explore replacement with a newer and fully supported model of iPad. The second generation iPad Pro is currently listed by Apple as "vintage", this being the step prior to being declared obsolete.