A couple of questions first:
1. What exact Mac model do you have?
2. What exact Mac OS are you running?
3. This is
critical: are you making backups to an external device? If you (hopefully) are, what software are you using for that?
Disk Utility does some "limited" disk cleanup. For getting rid of stuff that Disk Utility does not touch, here are some things you can do/use (make sure you have a recent backup
first):
1. You can actually do a good amount of disk cleanup on your own. A good place to look is in your Downloads folder. Another candidate is the "deletion" of EMails. When you delete an EMail, it is actually not removed from your system. If you actually want it removed, typically there is another menu choice/keyboard combination you need to choose/use. That varies for each EMail program. I use Outlook 2016 as my EMail client, and the process to have deleted EMails removed is actually quite easy. I do it just about every time I check my EMail on both of my Macs.
2. Here is a list (with links and comments) containing some excellent free programs:
Onyx - Available from here:
https://www.titanium-software.fr/en/onyx.html
Rock Solid, has been around a long, long time, and has had many positive reviews. I use it religiously (along with a commercial program entitled Tech Tool Pro). I would not be without either of them. In fact, I will not upgrade to a new Mac OS until there are compatible versions of both of them for the new OS (along with 4 other critical programs that I have). Note that there are different versions of Onyx available, for each different Mac OS. You would need to get the correct version for the Mac OS you are using.
AppCleaner - Available from here:
https://freemacsoft.net/appcleaner/
Another stellar performer! As you can see via that link, it will get rid of most stuff associated with an application that you wish to delete. Like Onyx, note that there are different versions for different versions of the Mac OS. You would need to get the correct version for the Mac OS you are using.
GrandPerspective - Available from here:
http://grandperspectiv.sourceforge.net/
Nifty graphical way to see which files are on your drive. Good way to identify large ones that you might not need.
Malwarebytes - Available from here:
https://www.malwarebytes.com/mac/
Good to use if you see adware and/or suspect you might have a virus. It also is good to run it every so often, even if nothing is wrong.
ClamXAv - Available from here:
https://www.clamxav.com/
More extensive than Malwarebytes in terms of finding viruses. You can use it in demo mode, and it still has just about full functionality.
3. As mentioned above, I use an excellent commercial program called Tech Tool Pro (
https://www.micromat.com/products/techtool-pro) for doing some additional maintenance and repairs (and some disk cleanup). Two other good ones are Disk Warrior (
https://www.alsoft.com/diskwarrior/?gclid=EAIaIQobChMI9qzeqcSF2gIViWp-Ch0NngwsEAAYASAAEgJg7_D_BwE), or Drive Genius (
https://www.prosofteng.com/drive-genius-mac-protection-software/). Using any of those (in addition to your own efforts, and the free software I mentioned above) will go a long way to keeping your Mac "lean, mean, and clean".