I can't find the Install Package "04t8b000001FBRG".

同じエラーメッセージの質問がりました。

Trailhead チームにチケットを発行して対応してもらったみたいです。

https://trailhead.salesforce.com/trailblazer-community/feed/0D54V00007epmidSAA

also checked in my organization, on a new Playground, and received a similar error. So, indeed, it is necessary to submit a support ticket here to have them address this issue.

Please raise a ticket to the trailhead team using this link: https://trailhead.salesforce.com/help?support=home&category=Trailhead&casereason=Trailhead%20Technical%20Issue&questiondetail=Other%20Trailhead%20Technical%20Issue#cfPanel