I can only tell you that keeping my site 100% free of sponsored content (labeled or not) has not helped my site with Google ranking whatsoever - it is demoted to the ground. So having it full of spam content (I get those spammy emails about sponsored posts every day like most of us) would most likely make no difference.

Google ranking is surprisingly dumb.

I was an original Adsenser plus being a member of the UPS Club of hand-delivered USD 10+K a month earnings' cheque All was fine until 2010's image theft and then over the next 5 years earnings reduced drastically until I removed Adsense completely. My CTR reduced from, I think 7%, to under 1%, and with massively reduced page views it became pointless.

Even though I removed all advertising my rankings changed very little but whether this is applicable now I have no idea other than an educated guess it would not. Likewise whether adding ads makes any difference, and especially so sparingly, try it and see and let us know.

Well, it depends. If the sponsored content is not checked/verified for correct info/spammy sounding and not related to your niche, eventually this can hurt you but usually they demote the POST/PAGE, not your domain, but it counts as a strike against your whole domain regardless so if the strikes add up, boom.

Just make sure the sponsored posts are within your niche and are unique or mostly unique from other sites who are also accepting whomever contacted you.

If they are not labeled and you place dofollow links, that is exactly the pattern Google usually flags as paid link schemes. Even if you do it rarely, the problem is not the number but the intent. Sponsored content itself is fine, many news sites do it, but normally they mark it clearly and use rel sponsored or nofollow on the links. For Discover the bigger risk is trust signals. If Google starts seeing mixed editorial and hidden sponsored posts, the site quality perception can drop. If you really want to run them, keep them transparent and treat the links as sponsored.

Apart from the fact that you are required by EU law to label such articles (and that this also has something to do with integrity): As long as the article does not appear to be advertising, the links are integrated naturally, i.e., the anchor text in the article is not “Company XYZ” and the text fits in with the rest of your content (by which I mean: if you only publish short news items, an article that is not news will naturally stand out. And, if you write about lawnmowers, the article should be about that and not about doing laundry), Google cannot recognize this. Of course, you should not overdo it, but as a rule, this has no effect.