The example sentence in the (prohibition) な entry is unnatural/bad.

[Morgawr]

The first example sentence for the dictionary entry "な" (don't / prohibition) is:

本末を転倒するな

This is a reference to the yoji 本末転倒, however broken down in parts and used like this really is not common/is unnatural in Japanese (borderline incorrect).

There's a discussion with native speakers pointing it out in this reddit thread.

I think it would be better to remove this example sentence.

[stephenmk]

The comment in the reddit thread notes that the example is not formally incorrect. I haven't read the whole thread but there seems to be some discussion about what the native speakers consider to be the most natural phrasing: 「本末転倒なことをするな」, 「本末転倒になるな」, 「本末転倒にならないように気をつけてね」, etc.

So on the one hand, it can be difficult to craft sentences that sound perfectly natural to all native speakers. On the other hand, I don't think the example sentence is extremely unnatural to begin with. Shogakuan's Progressive Japanese-to-English dictionary has it as an example for 本末:

本末を転倒する
confuse the order of things／fail to put first things first／put the cart before the horse

The Google web n-gram corpus from 2007 also shows that the 「本末を転倒」 phrasing is about ten times less common than the 「本末転倒」 4-character idiom, so it's not exceptionally rare.

Google N-gram Corpus Counts
╭─ーーーーーーーー─┬───────┬───────╮
│ 本末転倒する　　 │   238 │ 74.8% │
│ 本末を転倒する　 │    80 │ 25.2% │
├─ーーーーーーーー─┼───────┼───────┤
│ 本末転倒しない　 │   224 │ 91.8% │
│ 本末を転倒しない │    20 │  8.2% │
├─ーーーーーーーー─┼───────┼───────┤
│ 本末転倒して　　 │ 2,510 │ 91.0% │
│ 本末を転倒して　 │   248 │  9.0% │
╰─ーーーーーーーー─┴───────┴───────╯

Crafting good example sentences is work that, even for native speakers, requires skill and experience. Native speakers passing by will not necessarily have that experience. As Jim Breen noted in 2021 about Kenkyusha's New Japanese-English Dictionary ("GG5"):

Building fit-for-purpose examples from scratch is actually quite a challenging task. Several of my acquaintances worked on this aspect of the GG5 and found it quite demanding.

The Tanaka corpus that comprises most of the example sentences in JMdict/Jitendex wasn't consciously designed for this purpose. I'm hoping that with the release of Jreibun in the future, we'll have a higher-quality basis to build from. Until then, I don't think it's worthwhile to nitpick the naturalness of existing sentences as long as they're serving their purpose sufficiently (e.g. demonstrating the "な" particle). In the end, people are going to develop a sense of style through massive amounts of exposure to the Japanese language, of which example sentences in the dictionary will only be an extremely small fraction.