Hello,
i installe SparkyLinux 5.7.1 but in aptus i can not install virtualbox
No, you can not install it now.
The virtualbox has been temporary removed from Debian Buster repos.
You have two solutions:
1. Temporary enable Debian Sid repos and install virtualbox.
2. or download virtualbox deb package for Buster from the VirtualBox project page and install it.
I tried numerous times to get kvm-qemu up 3 years ago stretch was in testng, I went with Virtualbox. However in my new ssd where Buster stable will go I did the live Debian Buster, and kvm-qemu came up easy. I had problems with the virtual box ppa. And my 3 y.o .vdi of Windows7 converted to qemu easy also.
So maybe try kvm-qemu. There will always be a clash of philosophy - views between Debian and VirtualBox.
The above option will get you virualbox. I had no problems with it so far in 3 years in Stretch.