The easiest way is with a second list that's empty:
<control type="list" id="6000">
<visible>Container.Content(seasons)</visible>
<itemlayout />
<focusedlayout />
<content sortby="year" sortorder="ascending">$INFO[Container.FolderPath]</content>
</control>
<control type="label">
<top>300</top>
<align>right</align>
<label>$VAR[Seasons_Year_Label]</label>
</control>
<variable name="Seasons_Year_Label">
<value condition="Integer.IsGreater(Container(6000).NumItems,1)">$INFO[Container(6000).ListItem(0).Year]$INFO[Container(6000).ListItem(-1).Year, - ]</value>
<value>$INFO[Container(6000).ListItem(0).Year]</value>
</variable>
That will return the year range for the seasons of a show when you are on seasons level ("2020 - 2023"). I used a variable so if the list only has one item, i.e. it's only got one season, you can have it show as "2023" instead of "2023 - 2023". Beacause the list is sorted by ascending order, you can get the year the TV show started just by using "$INFO[Container(6000).ListItem(0).Year]" by itself.
The list uses the Container.FolderPath of the listitem selected in your main list to look up the information. The reason to use a second list instead of just doing $INFO[ListItemAbsolute(0).Year]$INFO[ListItemAbsolute(-1).Year, - ] is that then it doesn't matter how your main list is sorted. Our secondary list will also be in ascending year order.
As a bonus, you can use this method to get information about the child level items as well, e.g. get info about seasons on at the show level, or movies at the set level. All you need to do is change $INFO[Container.FolderPath] to $INFO[ListItem.FolderPath].
If you want to use this method for multiple scenarios, you can use a variable for the content path in the list, e.g.
<variable name="Hidden_List_Content_Path">
<value condition="Container.Content(sets) | ListItem.IsCollection">$INFO[ListItem.FolderPath]</value> <!-- get info about child level e.g. movies at the set level or if a set is selected if you have sets enabled in the movies level -->
<value condition="Container.Content(tvshows)">$INFO[ListItem.FolderPath]</value>
<value condition="Container.Content(seasons)">$INFO[Container.FolderPath]</value> <!-- get info about all your seasons e.g. year range at the seasons level -->
</variable>
