Google Apps Script for Google Spreadsheet. This onEdit function will identify Jira issue keys that are alone in an edited cell, and replace them with a HYPERLINK function with a link to your Jira installation.

Jira-hyperlink.js

// Jira-hyperlink from https://gist.github.com/mogsdad/1956f50b509b4f0e9ef44a6837fa52ae

const jiraUrl = "https://jira.example.com" // Top-level URL for our Jira instance

function onEdit(e) {
  var re = /^ *[a-z][a-z0-9_]+-\d{1,6} *$/gi
  var content = e.value;
  if (re.test(content)) {
    var cell = e.range;
    cell.setFormula('HYPERLINK("'+jiraUrl+'/browse/%BUGNUM%";"%BUGNUM%")'.replace(/%BUGNUM%/g,content.toUpperCase().trim()))
  }  
}

Here is a version that handles every cell in the whole range selection rather than top-left cell:

// Jira-hyperlink from https://gist.github.com/mogsdad/1956f50b509b4f0e9ef44a6837fa52ae

const jiraUrl = "https://jira.example.com" // Top-level URL for our Jira instance


function onEdit(e) {
  // AppScript execution log errors because e is undefined, not sure why it tries to call with undefined event.
  if (!e) return;
  
  const values = e.range.getValues();
  values.forEach((row, i) => {
    row.forEach((content, j) => {
      const re = /^ *[a-z][a-z0-9_]+-\d{1,6} *$/gi;

      if (re.test(content)) {
        const cell = e.range.getCell(i + 1, j + 1);
        cell.setFormula('HYPERLINK("'+jiraUrl+'/browse/%BUGNUM%";"%BUGNUM%")'.replace(/%BUGNUM%/g,content.toUpperCase().trim()));
      }
    });
  });
}