Thank you, I finally managed to have a working Vagrant version.
If anybody else is stumbling upon this thread:
Following
https://github.com/mysociety/alaveteli/issues/6110, after the initial error launching I did
vagrant ssh -c "sudo apt -y install linux-headers-amd64"
it first didn't help, then noticed
.vagrant.yml where the OS also needs to be changed:
os: buster64also, I found in some document that one also needs to run `
vagrant vbguest` besides installing the plugin. I also did that at some point, unsure if that helped.