Found a way to do what I was looking for. For anyone that is the “same boat”, I found this on this site[0]:
{{ $parts := split .Content "<!-- readmore -->" }}
{{ $summary := index $parts 0 }}
{{ $summaryHTML := safeHTML $summary }}
{{ if eq $summaryHTML .Content }}
{{ .Content }}
{{ else }}
{{ $summaryHTML }}
<a href="{{ .Permalink }}”>Read more...</a>
{{ end }}
[0] How to show the full post unless there’s a user defined summary in Hugo · Elliot Jackson