All descriptions on Apple Podcasts app are truncated and only show excerpts. Embedded hyperlinks not clickable

As you haven't posted the URLs of your feed and Store page I can only give you general answers.

In the iTunes Store page the description is drawn from the 'itunes:summary' tag in the top section of the feed. This is limited to about three lines and anything longer will be truncated.

When subscribing in iTunes, the subtitle is drawn from the 'itunes:subtitle' tag within the episode tag: there is only room for a short description and anything longer will be truncated; you can't avoid this - it's intended for a brief description. When clicking the 'i' button at the right-hand end of the subtitle line, the contents of the 'itunes':summary' tag are displayed. This can be quite long.

As to links, Apple say:

To include links in your description or rich HTML, adhere to the following technical guidelines: enclose all portions of your XML that contain embedded HTML in a CDATA section to prevent formatting issues, and to ensure proper link functionality. For example:

<![CDATA[ <a href="http://www.apple.com">Apple</a> ]]>

I haven't tested whether this works in iTunes: I don't use either version of the Podcasts app and things may be different there.

Apple's recent information omits the 'itunes:subtitle' and 'itune:summary' tags, substituting the 'description' tag (which it always used ro read in the omission of the summary tag): the older tags still work. it's not clear where the subtitle (if any) is supposed to come from. You may find their help page on interest:

https://help.apple.com/itc/podcasts_connect/#/itcb54353390

In fact your feed is at https://getcloseness.com/feed/podcast

You do have the 'itunes:summary' and 'itunes:subtitle' tags as well as the 'description' tag: they all have the same text, and they all use the enclosing CDATA tag.

Even so, when using html iTunes does not render it, though the Store does. For example, your episode's 'description' tag begins:

<description><![CDATA[<p>If you&#8217;ve ever secretly wondered what it&#8217;s like to be....

Here you are using the code for a 'right single quote', but it's the same as the standard keyboard single quote/apostrophe: ', which you could just as easily use.

The iTunes Store renders this correctly: subscribing in iTunes does not. iTunes still applies in all OSX systems prior to Catalina and on Windows: the Podcasts App replaces it on Catalina and iOS. This may render things better.

The description for the overall podcast is slightly truncated in the Store but can be displayed in full by clicking the 'more' link. It ends with a URL which is not a link because t does not start with http:// If it did I doubt it would work as a link, at any rate not pre-Catalina.

In all cases your subtitle is the same as your description, and is very long: this will always be truncated and would be better as a brief description. Your top episode's description ends with the code

…

which is for an ellipsis: this is not being rendered either and would be better achieved by typing three stops.

Loooking at your episode 'How to kiss properly' (ths first with an actual link anywhere in these tags), the 'description' contains a link to YouTube, but the 'itunes:summary' tag does not contain this and ends with the ellipsis tag - if the full text was there it would display though the link might not.

I was looking for a summary tag containing a link but there isn't one in the first few episodes (I don't fancy ploughing through the entire feed!). The description tags often contain a link, but as there is a summary tag it's that which is being displayed. This is in iTunes pre-Catalina: I can't answer for the new Podcasts app: but it does look as if Wordpress is sabotaging your attempts to get a full display of long tags (incidentally the Store is truncating the episodes' summary tags, but iTunes does not when subscribing).

Since you say you've seen podcasts with functioning links it's evidently possible, at least in the new apps: but you will need to sort out Wordpress so that links and full text get into the summary tags (or you remove the summary tags and rely on the description tags - though you will still need separate subtitle tags to avoid truncation).