[Actual Results]
When an email is created from the timeline of the [Opportunity] record, the record is automatically registered as [To], and the record set as [To] has priority when searching for a template.
Therefore, the template of [Opportunity] is not displayed even if the [Related] record is set.
When creating an e-mail from the timeline, the template of [Opportunity] can be used by deleting the value of the [To] field that is automatically registered and setting the [Related] record.

[Expected Results]
When composing an email from the timeline, [Opportunities] templates should be displayed by search.