You can achieve this by modifying your WF, adding a validator setup making Comments required and associate the transition with a custom pop-up screen. In the pop-up screen, you don't need any field. By default, when a screen is created just for the WF transition, the Comments field is automatically added behind the scene.
NOTE - We have an Add-on (JMWE) where it provides us with an validator making Comments required. https://marketplace.atlassian.com/apps/292/jira-misc-workflow-extensions-jmwe?hosting=cloud&tab=overview This is an excellent add-on for any Jira/JSM envs, making the WF customization easier without custom coding.
So when an issue moves into RESOLVED, the custom pop-up screen will be displayed and one cannot complete the transition unless comments are entered.
Hope this helps.
Best, Joseph Chung Yin
Jira/JSM Functional Lead, Global Infrastructure Applications Team
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