redstrate.com/themes/red/layouts/shortcodes/insert-pic.html

{{ $name := .Get 0 }}
{{ $alt := .Get 1 }}

{{ $path := printf "pics/%s" $name}}

{{ with resources.Get $path }}
<picture>
{{ $avif_path := replace . ".jpg" ".avif "}}
{{ with resources.Get (strings.TrimSpace $avif_path) }}
    <source srcset="{{ .RelPermalink }}" type="image/avif">
{{ end }}
<img alt="{{ $alt }}" class="gallery-img page-pic" width="{{ .Width }}" height="{{ .Height }}" src="{{ .RelPermalink }}">
</picture>
{{ end }}