“In this world you will have trouble. But take heart! I have overcome the world." John 16:33b

Yes, sometimes, but trusting God is more about realizing that whatever the in-between looks like, the outcome will be for the best. Therefore you can actually live life in fullness, by living without fear. Otherwise your life is already taken by Covid19.

"And we know that in all things God works for the good of those who love him, who have been called according to his purpose."
Romans 8:28

"Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God. And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus."
Philippians 4:6‭-‬7

Good question, but it isn't about mere belief, but about what is true. The difference becomes evident with spiritual discernment. Until it is granted to you, you won't see the difference. Much is written on this in the first chapters of 1 Corinthians, starting in verse 1:18 (https://www.biblegateway.com/passage/?search=1%20Corinthians%201&version=NIV). Also, the Bible says "Seek and you shall find" so it's not like God is keeping the truth from anybody, though truth is a bigger concept than mere knowledge. In other words, God knows who is really after things for the right reasons and not merely to usurp some power, glory, or other selfish benefit.

As for those like you, I believe that deep down you are not as satisfied as you think, or at least not as much as you could be. Trials have a way of revealing the weaknesses that have been smoothed over in our hearts that we don't even know are there, and judgment is here so it might even happen in the near future. However it happens, God loves you too. He will give you a chance, be it in this life or the next to see the truth if you really want it.

"Then that means that God can't blame or punish anyone for not using it if he doesn't give it to them."

That would indeed appear to be true:

"(Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law. They show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts sometimes accusing them and at other times even defending them.) This will take place on the day when God judges people’s secrets through Jesus Christ, as my gospel declares."
Romans 2:14‭-‬16

"There are people who have earnestly and sincerely searched, and haven't found god or good evidence for him."

1) You don't really know how sincere they are or not. Satan blinds many with pride.
2) Their stories aren't done and God's timeline isn't ours. He isn't as concerned with if you are 9 or 90 as Christians themselves are because He knows the outcome.

"I'm not saying my life is perfect and that I don't have problems, but I do have a very high level of satisfaction in my life. As much as or more than when I was a Christian."

Many of the things that seem to satisfy in this life are unreliable, or unimportant in reality. Families can die. Legacies can be forgotten. Societal advancement can be erased. But God respects free will. I've heard via prophecy that God will let the fallen angels have this creation (universe) that they want. It will wind down and disappear, so their desire is foolish, but He still respects their right to choose their course.

"Also, none of that refuse my claim that somebody who worships a different God can say that their God gives them peace and fulfillment and you wouldn't really have any way of demonstrating that they're wrong."

I can't demonstrate it, but it will be shown. Real peace is spiritual and based on truth. All other peace is temporary/circumstantial and/or based on illusions. When circumstances become difficult, the insufficiency of their peace will be shown. Real peace requires 100% certainty in one's source, not 99.999% That isn't possible without Holy Spirit, and can be verified only in the hottest of fires. You can claim something else is possible hypothetically, but you really don't know because you've never known real peace or where it comes from. I do.