Not saying monopolies aren't a problem, but I'm not able to connect the dots on how monopolies are responsible for the inflation since 2021 unless monopolies have gained power since then.
Otherwise shouldn't we expect the inflation to have started before covid?
Means plus opportunity. During COVID, there were legitimate shortages and supply chain disruptions that caused price spikes and (in some cases) additional profits. When these subsided, firms now had the opportunity to test whether holding prices at this newly elevated level would be tolerated. When the state failed to act to stop them, instead colluding with firms and the media to blame the price increases on thing like spent-and-gone stimulus and labor shortages, they saw they had a free hand to keep prices (and profits) as is. There was no guarantee that this would play out this way until it did, which these monopolies then took advantage of to keep prices artificially high.
There's one key mistake you're making in your assessment. That stimulus is not "spent-and-gone." That money continues to stay in circulation. You can see a graph of the monetary supply here [1]. And you can observe that inflation only started to get reigned in once the monetary supply started to decline. This is why many individuals tend to be against 'printing' money. It's not like people get a boost and things then go back to what they were before, but rather you now have trillions of more dollars floating about in the economy which will tend to drive prices up.
I'd also encourage you to look at the financials reports from most companies. If your profits increase by 5% at the same time inflation increases by 8% then you're both (1) getting absolutely economically wrecked, and (2) reporting 'record profits.' As companies are motivated to frame their earnings as positively as possible, this can be misleading to people who take those reports at face value.
Otherwise shouldn't we expect the inflation to have started before covid?