Curl & libcurl3 held back, possibly by .net core

Question

When I try to upgrade my packages, I receive a message that curl and libcurl3 have been kept back. I did not do this myself.

Referring to "The following packages have been kept back:" Why and how do I solve it?, when I try to apt install curl and libcurl3 it fails as curl depends on libcurl4.

When I try to install libcurl4, I receive the following output:

The following packages were automatically installed and are no longer required:
  aspnetcore-store-2.0.0 aspnetcore-store-2.0.3 aspnetcore-store-2.0.5 dotnet-host dotnet-hostfxr-2.0.5 dotnet-runtime-deps-2.1.0-rc1 liblttng-ust-ctl4
  liblttng-ust0 liburcu6
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  curl
The following packages will be REMOVED:
  dotnet-runtime-2.0.5 dotnet-sdk-2.1.4 libcurl3
The following NEW packages will be installed:
  libcurl4
The following packages will be upgraded:
  curl  

Uninstalling .NET Core is not an option. Can I safely ignore the fact that curl has been held back? Will .NET Core eventually be updated to use the new curl version? Is there a third option?
Thanks in advance!

Ubuntu 18.04. Latest updates. Dot Net installed via apt from the official repo

As requested, apt-cache policy dotnet-runtime-2.0.5 dotnet-sdk-2.1.4 curl libcurl3 libcurl4:

dotnet-runtime-2.0.5:
  Installed: 2.0.5-1
  Candidate: 2.0.5-1
  Version table:
 *** 2.0.5-1 100
        100 /var/lib/dpkg/status
dotnet-sdk-2.1.4:
  Installed: 2.1.4-1
  Candidate: 2.1.4-1
  Version table:
 *** 2.1.4-1 100
        100 /var/lib/dpkg/status
curl:
  Installed: 7.55.1-1ubuntu2.5
  Candidate: 7.58.0-2ubuntu3.2
  Version table:
     7.58.0-2ubuntu3.2 500
        500 http://au.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
     7.58.0-2ubuntu3 500
        500 http://au.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
 *** 7.55.1-1ubuntu2.5 100
        100 /var/lib/dpkg/status
libcurl3:
  Installed: 7.55.1-1ubuntu2.5
  Candidate: 7.58.0-2ubuntu2
  Version table:
     7.58.0-2ubuntu2 500
        500 http://au.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
 *** 7.55.1-1ubuntu2.5 100
        100 /var/lib/dpkg/status
libcurl4:
  Installed: (none)
  Candidate: 7.58.0-2ubuntu3.2
  Version table:
     7.58.0-2ubuntu3.2 500
        500 http://au.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
     7.58.0-2ubuntu3 500
        500 http://au.archive.ubuntu.com/ubuntu bionic/main amd64 Packages  

dpkg-query -s dotnet-runtime-2.0.5 dotnet-sdk-2.1.4:

Package: dotnet-runtime-2.0.5
Status: install ok installed
Priority: standard
Section: libs
Installed-Size: 59412
Maintainer: Microsoft <dotnetcore@microsoft.com>
Architecture: amd64
Version: 2.0.5-1
Depends: libc6 (>= 2.14), libcurl3 (>= 7.16.2), libgcc1 (>= 1:3.0), libgssapi-krb5-2 (>= 1.14+dfsg), liblttng-ust0 (>= 2.5.0), libstdc++6 (>= 4.8), libunwind8, libuuid1 (>= 2.16), zlib1g (>= 1:1.1.4), libssl1.0.0, libicu57, dotnet-hostfxr-2.0.5
Description: Microsoft .NET Core Runtime - 2.0.5 Microsoft.NETCore.App 2.0.5
 .NET Core is a development platform that you can use to build command-line applications, microservices and modern websites. It is open source, cross-platform and is supported by Microsoft. We hope you enjoy using it! If you do, please consider joining the active community of developers that are contributing to the project on GitHub (https://github.com/dotnet/core). We happily accept issues and PRs.
Homepage: https://dotnet.github.io

Package: dotnet-sdk-2.1.4
Status: install ok installed
Priority: standard
Section: devel
Installed-Size: 196263
Maintainer: Microsoft <dotnetcore@microsoft.com>
Architecture: amd64
Version: 2.1.4-1
Depends: dotnet-runtime-2.0.5, aspnetcore-store-2.0.5
Description: Microsoft .NET Core SDK - 2.1.4
 .NET Core is a development platform that you can use to build command-line applications, microservices and modern websites. It is open source, cross-platform and is supported by Microsoft. We hope you enjoy using it! If you do, please consider joining the active community of developers that are contributing to the project on GitHub (https://github.com/dotnet/core). We happily accept issues and PRs.
Homepage: https://dotnet.github.io/core

Answer 1

The issue came from an incompatibility between dotnet-runtime-2.0.5 and libcurl4. The current version of dotnet-runtime uses libcurl4 as opposed to libcurl3. I believe the old version of the runtime was a remnant from the upgrade to 18.04 from 17.10.

I readded the microsoft repo, removed dotnet-runtime-2.0.5 and installed dotnet-runtime-2.1, which allowed me to then upgrade curl and in turn installed libcurl4
The specific steps involved are:

wget -q https://packages.microsoft.com/config/ubuntu/18.04/packages-microsoft-prod.deb
sudo dpkg -i packages-microsoft-prod.deb  
sudo apt update

This deb automates the adding of the .NET Core repo to the system. Then I removed the old packages and installed the new versions with:

sudo apt autoremove dotnet-runtime-2.0.5
sudo apt install dotnet-runtime-2.1 curl