Please try the content of this link: Discourse 调整论坛内嵌bilibili视频播放器大小 - #6 by honeymoose - Discourse - iSharkFly
I can use it myself, but it’s still not very user-friendly for ordinary users. The plugin used to work well, but suddenly it doesn’t.
The plugin has likely not been updated for a long time.
With the update of Discourse, the plugin should no longer be usable.