So this 2011 laptop can still boot normally? It is only when you attempt to boot into Recovery Mode that you receive the circle with the line through it?
Why do you want/need to boot into Recovery Mode? Perhaps the same issue is causing both problems.
Try booting into Internet Recovery Mode using Command + Option + R assuming you are running macOS 10.12.4+ so that you can access the online macOS 10.13 installer.
The circle with line through it indicates a bootable macOS is seen, but it is not compatible with your Mac perhaps because it is damaged. If you are booting into local Recovery Mode using Command + R, then you are booting to those same damaged files.
Otherwise if this laptop still boots normally, then I highly recommend you create a bootable macOS 10.13 USB installer using the instructions in this Apple article while you still can:
Create a bootable installer for macOS - Apple Support
The 10.12 installer is broken when it comes to creating a bootable USB installer, but can be fixed using the information here:
Instructions to fix the macOS 10.12 Sierra installer
However, unless you have a third party app which is not compatible with 10.13 High Sierra, then I would recommend using High Sierra instead since that is the last OS compatible with a 2011 Mac.