Because then you have two things in front of the verb: the adverb "normalerweise" and the pronoun "ich". So the verb is in the third position in your sentence, but it has to be in the second position in a main clause.
You can say: "Ich esse normalerweise Frühstück", "Frühstück esse ich normalerweise", "Normalerweise esse ich Frühstück", "Frühstück esse normalerweise ich" - but the "esse" is always the second thing in the sentence.
And like with most adjectives, gewöhnlich can also be an adverb.
Wenn er kommt, isst er gewöhnlich Nudeln. "When he comes, he usually/ordinarily eats noodles."
(As an adjective, it would be inflected: Wenn er kommt, isst er gewöhnliche Nudeln. "When he comes, he eats ordinary noodles.")
I notice in German a lot of adjectives also act like adverbs?
That's right! Most adjectives can also be used as adverbs -- just take the bare adjective stem without any ending.
(This causes Germans who want to learn English problems; they end up saying things such as "he can sing good" because they aren't used to distinguishing adjectives such as "good" from adverbs such as "well".)
There is a subtle difference between gewöhnlich and normalerweise. Refer to this link: https://german.stackexchange.com/questions/63261/difference-between-normalerweise-and-gew%C3%B6hnlich
Can we put Normalerweise in a diffent position so to keep "ich esse" order in this sentence?
From a purely grammatical point of view, you could say Ich esse normalerweise Frühstück.
But from a pragmatical point of view, that doesn't sound like a natural thing to say, at least not to me -- I would put normalerweise at the beginning, as the topic, in this sentence.
I must disagree. "Having breakfast" is by far the most usual phrase one would use in English for eating it. Similarly, the main meaning of "having breakfast" is "eating breakfast", and it's "having it in my possession" that would have to be implied by the context, not the other way around.
Perhaps, but there is also the fact that getting the meaning right and getting the translation right are sometimes the difference between a wrong and right answer.
For instance, I would presume that a more accurate translation for "I have breakfast" would be something like "Ich frühstücke". If they went out of their way to say "Frühstück essen", I think they expect you to go out of your way to say "Eat breakfast" in English too.
in the earlier lessons. Fruhstuck was a stand alone word that could mean breakfast or eat breakfast.
Eh? No. Fruhstuck isn't a German word at all.
There is a noun Frühstück (with ü, not u) which means "breakfast".
(If you can't type the ü, then write ue, as in Fruehstueck.)
The verb is frühstücken with small f and with an ending that depends on the subject: ich frühstücke, du frühstückst, ....
Kind of like how "breakfast" in English can be a noun or (albeit more rarely) a verb -- but you can't say "he breakfast": it has to be "he breakfasts" with the appropriate verb ending.
Why not just Normalweise Fruhstuck ich.?
The adverb is normalerweise with -er- in the middle.
And if you want to use a verb, you have to have the appropriate ending: Normalerweise frühstücke ich. "Normally, I breakfast."
Or you could use the noun, in which case you need another verb: Normalerweise esse ich Frühstück. "Normally, I eat breakfast."
Should "normalerweise" not come directly after the verb, because it is an adverb?
The default place for an adverb is right after the verb, but another possibility (depending on the meaning of the adverb and the emphasis you want to place on the sentence) is in the first position of the sentence, before the verb.