This might be the case for the iPhone. I'm skeptic that this is a general practice because on the surface, customers would just migrate to competing products...
Maybe this practice is common for products that are in the lead/have a monopoly?
From the Daily Mail:
A new study is backing up long held suspicions that Apple slows down older models of its iPhones to encourage users to buy a new release.
In answer to the stated, rather than the implied question, the thing you're talking about is known as Planned Obsolescence. There are all sorts of indications that it happens sometimes. Admittedly, wikipedia is a very weak source, but the fact that there's an in-depth page on the practice, with a significant number of references, breakdown of different subtypes, and some historical analysis seems like a fairly reliable indication that it exists as a thing and is done sometimes in some places.
for a couple of more specific, reliable links:
Consumer Reports talks about a HP making a $5M settlement WRT printers that consumed ink cartridges more quickly than they should have.
https://www.consumerreports.org/cro/news/2010/11/hp-inkjet-printer-lawsuit-reaches-5-million-settlement/index.htm
The initial proposal (back in 1932) https://web.archive.org/web/20120819154515/http://upload.wikimedia.org/wikipedia/commons/2/27/London_%281932%29_Ending_the_depression_through_planned_obsolescence.pdf
IEEE talks about an early case, generated by collusion between major lightbulb manufacturers https://spectrum.ieee.org/geek-life/history/the-great-lightbulb-conspiracy/
Overall, it looks like in the current day, companies tend to avoid obvious cases of self-sabotage. Evidence suggests that it still happens (as in the case of HP), but is relatively rare, perhaps because they're punished (by the consumer and/or legal system) when caught. They're much more likely to degrade things in more subtle, defensible ways. In particular, a number of modern alterations offer some defensible advantage or other (slimmer, lighter, or whatever), while making repair and maintenance more difficult or impossible. Still making their product shorter-lived in order to reap the benefits of more frequent replacement, but in a manner much easier to explain away.
Snopes covers this study quite well, which points out it produces no actual evidence that Apple is doing anything of the sort. What the study has proven is that people may generally be a bit more sensitive to the perceived 'slowness' of current generation Apple devices whenever Apple announces a new release.
The study (also featured in the NYTimes) looked at no source code nor did it study any technical feature. Rather it looked at Google Search trends related to specific keywords (e.g. "iPhone slow") and found a correlating increase in searches around Apple product launches.
For the more general question, yes, planned obsolescence is a thing and not just because companies want to make money (though that can be a motivating factor). For some products, making a cheap, disposable model is more economically feasible than making a rugged one that would last a lifetime. The general example for this is a laser pen that etches writings into paper (which would be prohibitively expensive the first time you misplaced it) versus a stick of wood with a graphite core.
The question is about sabotage before sale, but the example given is Apple slowing phones down after they have been sold.
For examples of products sabotaged before sale, see DRM systems. Many products include DRM to prevent unauthorized copying or cheating (e.g. in online games), but it also tends to make the product worse.
Defects introduced by DRM include poorer performance in games and the inability to exercise your legal rights to make backup copies and format shift. Systems that require online authentication can cause the product to stop working completely when the service inevitably shuts down.
Another example is adding dots or other defects to movies to help determine where pirate copies originate from.
