I know that "myself" is a reflexive pronoun and can also be used for emphasis. When writing something to the tune of "I myself would love to go hiking." Wouldn't it be proper to use it as an interjection "I, myself, would like to go hiking." An interjection of this sort would typically clarify to whom the pronoun is referring, however "I" is already a clear indicator of who I am, without the "myself" attached.
TL;DR: Shouldn't I be using interjection commas for the phrase "I, myself, ..."?
What you are observing in this sentence is not an interjection. However, your instincts are right with regard to the behavior of "myself" here.
This sentence exhibits a case of an intensive pronoun (Wikipedia). (Specifically, it is an intensive reflexive pronoun.) Unlike purely reflexive pronouns, which are crucial to the meaning of a sentence, intensive pronouns simply add emphasis, exactly as "myself" does here. An easy way to distinguish a purely reflexive pronoun from an intensive one is to remove it from the sentence, and see if it still makes sense.
As it is not an interjection, it does not require the use of the commas. Furthermore, here's another English SE question about reflexive and intensive pronouns. See ScotM's answer regarding the use of commas with such pronouns.
While interjections is a heterogeneous category of words, I doubt that "myself" can be regarded as one. As a test, try replacing "I" in your example sentence with different pronoun. You will notice that "myself" will need to be replaced depending in the pronoun: "You yourself", "he himself", etc. I see no reason why interjections would need to change depending on the subject or the preceding personal pronoun. The reflexive pronoun is added to intensify the preceding pronoun. This type of pronoun is therefore sometimes called an intensifying reflexive pronoun. See also Intensifiers and Reflexive Pronouns in The World Atlas of Language Structures Online, which also gives examples in other languages.
Other examples (emphasis added):
Interjections are determined by usage. Any word or that is "thrown into" a sentence to express emotion or sentiment is an injection.
I hurried but, bad luck, missed the train.
I have never heard "myself" used as an interjection, but I have heard fairly random things like "whore" and "cheese and cracker" (presumably a minced oath for "Jesus Christ") and even nonce words like "wha".
In the sentence "I myself would love to go hiking", "myself" is an appositive, and so can optionally be set off by commas to emphasize its non-restrictive nature, so
I myself would love to go hiking, but my wife isn't feeling well.
but perhaps
I, myself, would love to go hiking, but can understand why other people might prefer a less-strenuous activity.
The word "myself" is often tautological and unnecessary, both grammatically and stylistically. In sentences like the one you use in your question, and "I wouldn't do that myself", the best advice is to not use the word "myself". I never use it myself.
