> I think it is quite clear that is what the text implies especially if you read from verse 19 to 21. Would be glad to hear if you have any reasons to suggest otherwise.
Romans 1 is where Paul is offering a diagnosis of the human condition: humans are in rebellion against their Creator, and God will judge such rebellion. The Jews often railed against the godlessness of the Gentiles, but Paul is setting them up to show them they are as guilty as everyone else (Rom. 2.1). And then chapter 3 puts the nails in the coffin: We are all missing the target.
So let's go back to v. 18 (of Rom. 1). God's wrath falls on all rebels, regardless of religion, nationality, or race. It's not a petulant, immature, emotional, vengeful rage, but instead a wrath of reason and law. It's true justice at work. And who is it against? People who knew but ignored, who took what was out in the open and tossed it under the carpet to hide it and desecrate it.
v. 19: The rebels knew better. It’s not as if God’s character or his loving desires for people were a big secret. God had made himself evident enough to be perceived on some level.
What Paul is referring to is natural revelation: God regularly and consistently gives things to men that betray a divine source: conscience (2.14), a moral sense (1.32), the natural world (1.20), guilt (1.18-19), and knowledge and truth (1.18-19). These are what are "made plain" to people.
Then v. 20 speaks of his "invisible attributes" that are clearly seen. I take this to mean things like order, regularity, predictability, purpose, beauty, and intelligence.
All of these elements point to a divine source. They make someone go, "You know, God is a reasonable source for all of these phenomena." Our senses and our science show us what the world is like, and our intelligence helps us proceed from the natural world to God, from effect to cause. The knowledge of the world we live in motivates us to seek to know what is beyond this world. The created universe opens one's mind to what must lie behind it.
v. 21: People make a choice. Though there is evidence of God, that evidence is refutable. Though God has revealed himself through more than natural revelation, but also through special revelation, that evidence is also refutable. (When it comes right down to it, all evidence in all of our disciplines is ultimately refutable. People make a choice what to believe.) Paul argues that people had enough evidence to go on as far as not just believing in God but knowing him, but intentionally rebelled and followed a path of their own choice. Because they rejected Truth, their thinking and knowledge became perverted (corrupted and distorted from its original meaning). I guess we would say it became secular: certainly still knowledge and truth, but "futile"—missing pieces that are supposed to be there. They were living in the shadows, only seeing part of the picture.
> It is a good question but God does not answer this question in an anymore meaningful manner either. It just regresses it to the question of "Why is there God rather than nothing"?
Correct. Something has to have always been eternal, whether matter, energy, some quantum something or other, God, or something else. Nothing can self-generate out of nothingness. Either nature was there (energy, etc.) and it "Banged," or else nature was not there, and something outside of it made it "Bang." So we have to wrestle with the question of causality, because anything that begins to exist has to have a cause.
On top of that, though, science tells us that first causes are always personal causes. We know of nothing that shows us otherwise.
When it comes right down to it, there is a natural and high connection between theism and causality: intelligence, personality, purpose, intent, freedom, power, and laws. It is very unlikely that a universe would exist uncaused, but rather more likely that God would exist uncaused. Theism also has sufficient prior probability (simplicity of explanation) and complete explanatory power. The intrinsic probability of theism, relative to other hypotheses about "Why is there something rather than nothing," is relatively high.