A few examples that have caused me some confusion over whomever/whoever usage

Every time I think I have a solid grasp of the whomever/whoever rules, I come across some online examples that conflict with what I've learnt. For instance:

https://www.businesswritingblog.com/business_writing/2013/04/tricky-pronouns-whoever-and-whomever.html

In this article, the following sentence is included as question #7 in the test at the end:

"Whoever/Whomever the CEO recommends will undoubtedly be considered for the position."

According to the author, the correct word is "Whomever", but this contradicts what I've learnt elsewhere. The way I see it, the verb "will" needs a subject pronoun, and so the word needed is "Whoever". The reasoning the author has given in the comments section below the article is that the pronoun is the object of the verb "recommends", but I thought "the CEO recommends" is supplementary and doesn't affect the sentence.

Likewise, in this example of my own, I would also use whoever:

"Please give the jewellery box to whoever you think is the most trustworthy."

https://www.toppr.com/guides/english-grammar/confusing-words/whoever-vs-whomever/

This page features "Give it to whomever." as an incorrect example, which I don't think is right because, using the he/him substitution rule, it would be "Give it to him." At the bottom of the article, the list of correct examples includes "Jenna should give the medal to whomever she thinks deserves it." Similar to the above, I'm not sure this is right because I think that "whomever" is the subject pronoun of "deserves" and, therefore, should be whoever.

Please may someone verify whether the examples from the sources are correct or incorrect?