Multi unit buildings are not great for DIY projects. You don't even say what brand, of cooktop. I'd at the least ASK where you purchased.

Fire power seems the least of the concern. Ask the local gas company..... often they will send someone out.

https://www.stromquist.com/blog/50/gas-regulator-sizing

Did the gas pro mention any issue when this was installed. BTW gas hook up IMO is never a good DIY project. As mentioned get a pro

The cooktop was installed by a professional but he didn't check the original regulator size, it is a Bluestar 22k btu cooktop, it's working right now but it seems the flame is weaker than I've expected for a 22k btu, so that makes me wonder if that's because I had the wrong regulator

Nice to see the "pro" read the specs : )

Really . Call him back and do this right.

I'm just wonder if the regulator size will make a difference of my flame power, if not I'm just gonna keep it this way because everytime I need do something in my condo I have to submit an application and wait for a week for them to get approved, it's really annoying.

It's ANNOYING??? Seriously?? I'll have my sister call you. She can tell you about the fire a neighbor started ..when her brother ( unapproved) was doing plumbing work. The building burned, 14 people went to work and came home to NO home hours later.. My sisters cat perished in the fire. It took 18 months for a rebuild and insurance NIGHTMARE followed for all.

"Arrogant" starts with the same letter as ANNOYED. BE BOTH, YOU ARE DEFINITELY THE FIRST.

There are reasons for rules, restrictions, permission slip approval. To save other owners from folks like you. You don't get to decide what is dangerous/benign...or otherwise.

Theoretically, through the same size orifice, the pressure from a 4" water column regulator will flow 80% what will flow from a 5" water column regulator. That may be why you are seeing a lower heat output than you expected. Whether the increased output you would get with a 5" regulator is worth the hassle you describe, that's going to be up to you to decide. There is no safety issue using the 4" regulator, though.