Create a helper class and define in function in helper. Then you can use where ever in those Magento project.

Helpers are usually used as elements **that are global and always available.**

Magento 2 Helper contains functions and methods that are commonly used throughout the application. Methods that are declared as Helpers can be called from `any template file, block, model, controller class` or even from another helper in Magento 2.

For more detail refer: https://www.mageplaza.com/devdocs/create-helper-class-magento-2.html

**Updated solution:**

you can get helper class valuea  in template like below code

    $this->helper('Vendor\Module\Helper\Data')->methodname();