Cannot install Monterey OS? I found a solution!

I had Mojave and I wanted to update to Monterey(or any other OS compatible with 2015 MacBook Pro15 inches) . I had at least 60 gb free on ssd , I tried many times, but I couldn't , got a lot of error messages etc.

So, I reinstalled Mojave, command+R , reinstall macOS Mojave( NO, it will NOT delete the contents of your ssd, it will just refresh the OS) . After that my MacBook Pro 2015 did some security updates and allowed me to do the update to Monterey without any problem.

Have fun!