You need to differentiate between the monthly security updates released by Google and app updates that get released by app developers. The monthly security updates pertain to the installed Android operating system on your phone. Those are separate from the various apps you've installed on your phone. An app update, like your banking app, only becomes available when its developer releases it, so that may be only every few months or weeks, or every few days when there's some urgent need that pops up.
Google releases security patches every month, it's unfortunately then the responsibility for the manufacturer and/or carrier to actually distribute them to us, the phone owners. In your case, it sounds like the manufacturer has chosen to support their phone they sold you up until 2026, so at that point your phone's Android OS will no longer receive those monthly patches, despite the fact that they will continue being available on a monthly basis. A lot of people blame Google about this issue but it's the manufacturers and/or carriers that have failed on their responsibilities.
But most app developers aren't so fickle. Apps tend to get updates for quite a bit longer than OS updates. Often years longer. So after 2026 your phone's Android OS won't be getting updates. but your banking app, along with other apps, will.