As with other posts in this stack exchange, I'm having issues with installing python3-dev on a fresh install of Ubuntu (18.04) that is running a pre-installed python3 (3.6.9-1~18.04). Many of the recommended fixes in those posts that I have tried have worked, such as uninstalling and reinstalling python3. I've had to restore my laptop to the factory defaults twice now because apt ended up breaking much of the operating system by modifying python3. Aptitude also could not resolve the conflicts.

More specifically, when I attempt to do sudo apt install python3-dev I get the following:

Reading package lists... Done
Building dependency tree      
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 python3-dev : Depends: python3 (= 3.6.5-3) but 3.6.7-1~18.04 is to be installed
               Depends: libpython3-dev (= 3.6.5-3) but it is not going to be installed
               Depends: python3.6-dev (>= 3.6.5-2~) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Here is the output of running sudo apt update:

Hit:1  stable InRelease
Hit:2  bionic InRelease                    
Hit:3  bionic InRelease                    
Ign:4  bionic-oem InRelease            
Ign:5  bionic-dell-beaver-osp1-gendry InRelease
Hit:6  bionic-oem Release
Ign:7  bionic-dell-service InRelease
Hit:9  bionic-dell InRelease
Hit:10  bionic-dell-beaver-osp1-gendry Release
Hit:12  bionic-dell-service Release
Reading package lists... Done
Building dependency tree      
Reading state information... Done
All packages are up to date.

and the output for sudo apt upgrade:

Reading package lists... Done
Building dependency tree      
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

I'd appreciate any help in figuring out how I can resolve these issues. Upgrading to the latest version of Ubuntu (20.04) is not an option right now.