Here's my version. You presumably have something slightly different.

\procedure show-date(fmt) <$view tiddler={{!!selectedtiddler}} field={{!!selectedfield}} format="date" template=<<fmt>>>(not a date)</$view>

\procedure date-row(name, fmt)
<tr>
  <td><<name>></td>
  <td><$transclude $variable="show-date" fmt=<<fmt>>/></td>
</tr>
\end

Tiddler:
<$select field="selectedtiddler" default="">
    <option value="">(choose a tiddler)</option>
    <$list filter="[!is[system]]">
        <option value=<<currentTiddler>>><<currentTiddler>></option>
    </$list>
</$select>

<!-- Don't show the field drop-down if no tiddler is selected, since it won't contain any options. -->
<% if [all[current]get[selectedtiddler]!is[blank]] %>
Field:
<$select field="selectedfield" default="created">
    <$list filter="[{!!selectedtiddler}fields[]]">
        <option value=<<currentTiddler>>><<currentTiddler>></option>
    </$list>
</$select>
<% endif %>

<% if [all[current]has[selectedtiddler]has[selectedfield]] %>
<table>
    <tr>
        <th>Format</th>
        <th>Date</th>
    </tr>
    <$list filter="[prefix[$:/config/DateFormatter/Formats/]]" variable="currentFormat">
        <$transclude $variable="date-row"
            name={{{ [<currentFormat>removeprefix[$:/config/DateFormatter/Formats/]] }}} 
            fmt={{{ [<currentFormat>get[text]] }}}/>
    </$list>
</table>
<% endif %>