These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.21 s (backtrack: 1/20).



[ebuild  N     ] dev-lang/mono-basic-4.8-r1::gentoo  3206 KiB
[nomerge       ]  dev-lang/mono-6.14.1-r1::gentoo  USE="nls -doc -minimal -pax-kernel (-selinux) -xen" 
[ebuild  N     ]   dev-dotnet/libgdiplus-6.2::gentoo  USE="cairo" 2231 KiB
[ebuild  N     ]    dev-lang/mono-6.14.1-r1::gentoo  USE="nls -doc -minimal -pax-kernel (-selinux) -xen" 296571 KiB

Total: 3 packages (3 new), Size of downloads: 302007 KiB

 * Error: circular dependencies:

(dev-dotnet/libgdiplus-6.2:0/0::gentoo, ebuild scheduled for merge) depends on
 (dev-lang/mono-6.14.1-r1:0/0::gentoo, ebuild scheduled for merge) (buildtime)
  (dev-dotnet/libgdiplus-6.2:0/0::gentoo, ebuild scheduled for merge) (buildtime, USE=-minimal)

It might be possible to break this cycle
by applying the following change:
- dev-lang/mono-6.14.1-r1 (Change USE: +minimal)

Note that this change can be reverted, once the package has been installed.