Why TexStudio for MacOS is not being installed?
Do you wish to get a notarized / signed copy of the code - you can reach out to the people that package it and ask they sign the code.
If not, you would need to do the checking yourself and perhaps relax the gatekeeper settings. Since you don’t specify anything about which version of the OS / which version of the program, hopefully this general guidance helps you research what step to take next.
Here is my advice - if you’re not sure how to figure out a security error or just don’t want to be bothered, it’s best to not relax security / GateKeeper. It is a significant bit of responsibility to add and you lose that protection for all software - not just for this, so be sure to re-protect with GateKeeper as soon as you run software that can’t be bothered to protect you from malware.
Also - you could have legitimate malware and be one step away from unleashing it. Be sure you have a backup before relaxing Apple security in case you have a tampered product you downloaded. Just because it came from the proper web site, doesn’t mean that web site or your network wasn’t compromised.