I actually wrote a long rant on why I think OC's are not the same as story characters in the story section of my Guide to getting eyeballs on your Tapas comic.
Basically to summarise my feelings, I think that if you view a character as "your OC" it's very hard to have them face really negative consequences for their actions, change significantly or die, so it's best to keep OCs (static pet characters you "have" as a mascot) and story characters (dynamic characters who are a moving part in a narrative) separate.
Killing off a supporting character to motivate the protagonist is an ingredient that can be used really well, or can be a really crappy cliche, sometimes with unfortunate misogynist implications due to overuse if the character is the male protagonist's female significant other, which was so prevalent in 90s comics it even earned the specific name "Women in Refrigerators" or "Fridging". Having the villain kill the hero's under-characterised girlfriend so that he can be emotional (because of the unfortunate idea that was particularly prevalent in 90s comics that male characters are only permitted to be emotional in this kind of extreme situation) and feel motivated to defeat the villain can be very cheap and dehumanising, especially when it happens so much it's a cliche or trope. It doesn't mean that killing off characters is always bad... but it can be a really cheap way to get shock value, and if the character in question has little presence in the plot, no particular characterisation and you weren't really attached to them, it's not hard to do. It's true that because this is known as a cliche now that it's become a lot less common, with probably the last really noteworthy pointless female comics shock value death being Wasp getting eaten by The Blob in Ultimatum (a comic I think everyone can agree really sucked) back in... when was that, '06? I think it was in '06. Still, I think it's important to be aware of fridging as a concept just because it's such a good example of the cheap way to use disposable characters so that, regardless of the character's gender, people know to avoid overusing that particular tool.
A character death as motivation or to explore how grief affects people can be a really amazing tool if the character is meaningful and has had a personality and agency. Like the entire reason for the famous sudden and unexpected partymember death in the middle of Final Fantasy VII came about because the director experienced the death of someone close to him, and I think that death truly enriches the story of that game. It would not be as deep or moving a story or as memorable without it.
Then you have works that are kind of a mixture like the Harry Potter series, where some of the deaths are really intense and shocking and really seem to impact the plot, like Sirius or Cedric Diggory, but some feel arbitrary, rushed and just kind of thrown in for shock value, especially ones that happen offscreen, like Tonks and Lupin, Harry just kinda rolls up and "oh btw these two beloved major side characters are dead", the entire reason for them dying, according to Rowling, was to make their son an orphan like Harry, so in the epilogue we could see that he was doing okay despite being an oprhan.... Hmmmm... yeah I'm not really feeling it, I don't think it's a good enough reason to kill two really popular characters off-screen with no fanfare or time to really mourn and process it.
So yeah, while I'm not the kind of person who enjoys killing characters and I'm never going to be George R R Martin or anything, I think character death is a tool that a creator shouldn't completely write off. Death is part of the human experience after all.