Specifically it's meant for instructing "automatic clients known as crawlers" [0]. A crawler is defined by MDN as "a program, often called a bot or robot, which systematically browses the Web to collect data from webpages." [1]
As generally understood, wget is not a crawler even though it may be used to build one. Neither is curl. A crawler is a program which systematically browses the web, usually to build a search index.
I see no evidence that Perplexity's crawler is ignoring robots.txt, I only see evidence that when a user does a one-off request for a specific URL then Perplexity uses Chrome to access the site.
Basically, OP is using the wrong tool for the job and complaining when it doesn't work. If he wants to be excluded from Perplexity for one-off requests (as distinct from crawling) he needs to reach out to them, there is no applicable RFC.
[0] https://www.rfc-editor.org/rfc/rfc9309.html
[1] https://developer.mozilla.org/en-US/docs/Glossary/Crawler
If I know the creator of the page doesn't want his page used by my program I wouldn't do it.
>Discriminating based on User-Agent string is the unethical part.
Not being exploited by an AI company is unethical? Robots.txt is made for telling bot identified by user agent what they are allowed to read.