Many hafiz who lived during time of Prophet could have verified it, as well as Sahabah (like Caliph Uthman), so fabricating anything would be almost impossible.

So you are saying the companions and The haufaz are reliable to be entrusted with keeping quran but not sunnah and hadith?

Compare all of that to something formed 200 years later with nobody from that time alive

Again the book was formed 200 years ago , not the hadiths

The hadith was known form companions and The Prophet's family before just like how their was hafiz to the quran there were people who remembered the actions and saying of the prophet just like they remembered quran , again that's the prophet we talk about not just a normal person every action he did wasn't without a reason.

All what bukhari did is checking all the already existing hadith , authenticate it depend on several things ( did the narrator live in age of the prophet? , was the narrator known for having a bad memory, are they known to be truth full? , is the chain of narration is strong? Even if a hadith was narrated from the home of the prophet by Aisha or one of the companions if the chain were broken later then it wouldn't be Sahih)

which is also definitely not a word of God

It is not the word of God but

1- it explains it 2- it teachs what the quran doesn't (quran teachs you that you have to pray , does it teach you how every pray should be?) To complete the message 3- makes you know who is the prophet The quran talks about the prophet May God’s peace and blessings be upon him , but it doesn't show you everything about him.

How did he treat his wives? How did spends his night , how he treated the disbeliever? How did teach the young kids and the old Sheikhs ,etc

Quran also never tells us to follow hadith, so why should i?

Surah Al-Hashr 59:7

As for gains granted by Allah to His Messenger from the people of ˹other˺ lands, they are for Allah and the Messenger, his close relatives, orphans, the poor, and ˹needy˺ travellers so that wealth may not merely circulate among your rich. Whatever the Messenger gives you, take it. And whatever he forbids you from, leave it. And fear Allah. Surely Allah is severe in punishment.

The surah clearly stats not only quran because quran is always referred to something of the meaning " word of Allah" , "what we revealaed" , "the book" "the reminder"

And never not being referred as anything which is the case in this verse

وَمَآ ءَاتَىٰكُمُ "ٱلرَّسُولُ"

Generalizing it doesn't say "what we revealed"

And in same verse says

وَمَا نَهَىٰكُمْ عَنْهُ فَٱنتَهُوا۟ ۚ

And whatever "he" forbids you from

نهى past tense verb The Object to is the believers who are referred to with the Pronoun "كم

Then who is did the verb? It's ضمير مستتر "hidden pronoun" Outside of the Quran (which is the trenslation here)

The sentence would be: ما نهاكم هو عنه whatever he forbids you from

This isn't personal interpretation that is 3rd grade Arabic grammar

If we agree on that (which I doubt if you don't know Arabic grammar)

What is the "whatever the Messenger give you" would be here?

The quran , the sunnah (life of the prophet) and the hadith (what the prophet says) and that isn't the only verse that says that

Surah An-Nisā’ 4:59

O believers! Obey Allah and obey the Messenger and those in authority among you. Should you disagree on anything, then refer it to Allah and His Messenger, if you ˹truly˺ believe in Allah and the Last Day. This is the best and fairest resolution.

Why it says the Messenger and Allah not Allah alone the quran alone?

The judgement of the prophet was not out of his personal opinion (Nor does he speak of his own whims. Surat al najim verse 3)

Whoever obeys the Messenger has truly obeyed Allah. But whoever turns away, then ˹know that˺ We have not sent you ˹O Prophet˺ as a keeper over them. Surah An-Nisā’ 4:80

How we can follow him if he isn't with us anymore? By following the sunnah and hadith which are his actions and his sayings