According to this page:

After June 4, 2024 if you enter a situation where you typically would create a classic Slack app or custom bot, you won't be able to. You'll have to create a modern Slack app or use the automation platform.

Jira for Slack only supports classic app creation at this time:

“ To get started, first visit https://api.slack.com/apps?new_classic_app=1. Make sure you create the App with classic scopes as Slack has released a new permission model that's not compatible with this App at this moment.”

Update the plugin to allow integrating with modern app in Slack.