We have full sandbox copy from production and now we want backup of that sandbox and when I go to sandboxes in setup it is not allowing due to limitation of packages what we have. So is it possible to retrieve everything on my local system and later I will push that to git(please highlight what we dont have in backup if we do backup in this way? Mean will something will miss from there or it will be same as sandbox copy?). I get this message when I want to make copy of full sandbox. Thanks in advance.
You can use ANT to fetch full backup from Org and then you can upload to the Git/Versioning system.
You can check this github repository to fetch all metadata - https://github.com/mattandneil/metadata-backup