However, it appears that these tags are alphabetized before they're shown. This is problematic, as certain feeds (e.g. those from Tumblr) intend for feeds to be seen in a specific order.

I don't get it. Why the order is important?

For the latest entry of the sample feed provided, I can see this in the feed:

<category>tumblr tuesday</category>
<category>balatro</category>
<category>balatro joker</category>
<category>artists on tumblr</category>
<category>gaming artists</category>
<category>long post</category>

Which is rendered in alphabetical order in the web ui:

Oh I suppose that was a bad example—tried using a generic one without checking. Sorry about that.

Commonly, Tumblr tags are used for additional comments on posts and said comments can comprise multiple tags forming multiple complete sentences.

Example: This feed, latest post, and on my Miniflux instance.

Any update on whether this behavior might be adjusted?

I did some digging and found that commit 863a5b3 introduced the change in behavior. Would it be reasonable to revert this or make this behavior an option?

Seems reasonable. Maybe add a comment about not changing the order of the fields?

Seems reasonable. Maybe add a comment about not changing the order of the fields?

Just updated the PR!