I am certain that I don’t get everything right
Yes, you are wrong here for instance. You said your spirit cannot sin.
That means you don't know what "sin" even is, because the very definition of "sin" is "spiritual slavery".
John 8:34
31So Jesus was saying to those Jews who had believed Him, “If you continue in My word, then you are truly My disciples; 32and you will know the truth, and the truth will set you free.” 33They answered Him, “We are Abraham’s descendants and have never been enslaved to anyone; how is it that You say, ‘You will become free’?”
34Jesus answered them, “Truly, truly I say to you, everyone who commits sin is a slave of sin.
So, does Jesus think that there is a man somewhere forcing people to sin? No, Jesus is teaching that sin is spiritual slavery. That's what Paul explains, too.
Romans 6
4For sin shall not be master over you, for you are not under the Law but under grace.
Galatians 4
24These things serve as illustrations, for the women represent two covenants. One covenant is from Mount Sinai and bears children into slavery: This is Hagar.
25Now Hagar stands for Mount Sinai in Arabia and corresponds to the present-day Jerusalem, because she is in slavery with her children.
So, for Paul, sin is a "master" to the "slaves" which are those "under Law".
This is precisely what is described in Romans 7--sin is a "master" to people who are "under Law", who are "slaves" because the Law came in the increase the trespass Romans 5:20 by virtue of it being the strength of sin 1 Corinthians 15:56.
Romans 7-24
14For we know that the law is spiritual, but I am of the flesh,
sold under sin [sold like a slave]. 15For I do not understand my own actions. For
I do not do what I want [slaves don't do what they want] but I do the very thing I hate. 16Now if I do what I do not want, I agree with the law, that it is good. 17So now it is no longer I who do it, but sin that dwells within me. 18For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. 19For I do not do the good I want, but the evil I do not want is what I keep on doing. 20Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me.
21So I find it to be a law that when I want to do right, evil lies close at hand. 22For I delight in the law of God, in my inner being, 23but
I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members [slaves were often "captives", prisoners of war] 24Wretched man that I am! Who will deliver me from this body of death? 25Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.
Paul teaches that when he was in the flesh under the Law his inward person delighted in God's Law but it was not permitted to do it by reason of evil lying close by in the flesh--instead, he was forced to do what he did not want to do and what he hated and disagreed with. That is precisely what slavery is. The point is : there is no such thing as "sin" that is
not the spirit, because "sin"
is when the mind and spirit do what is contrary to their purpose (truth, service to God).