Zithro : And yet you continue trying to compile (possibly) incompatible softwares from source, instead of following the user guides, and despite our warnings.
You essentially say "I want to do some complicated stuff without understanding how it works, and quick please".
Are you reading my mind ? How can you know what I say ? I don't say or think what you think I think. My approach is something like this : to understand why I get that error,learning guides is not enough,or at least,I found that learning by doing is a good choice to learn for me. So,the chosen to recompile from scratch everything (Linux kernel,qemu,libvirt and virt-manager) is not a masochistic choice, it is useful for me because doing so,step by step,I will see what happens from a lot of different angles and I can learn the whole procedure evaluating a process at a time. Learning for me is important. If I do what you suggest as is,I will learn a few things,because probably your solution is correct,but I need to make errors before I can understand what's correct and what's not. Can you understand my point ? I spend my time reading,but I can't read everything since I don't know what's relevant and what's not. So before I read something I ask on various forums or ML what I should learn. That's because I need to focus my attention only on the points that are relevant to be able to achieve the project. This is important to avoid reading a lot of useless things that would lead me astray. With that said,I have understood what to do,more or less. I should install a debian version that has a 5.4 kernel on board. I don't know which release could be. I hope that it has a version of qemu minor than 5.2,otherwise it will not work. If it is 5.2 or greater,I don't know what to do. Maybe I will try to recompile qemu 5.1 to see if it can be good with a 5.4 kernel shipped by that version of Debian. For sure I will also install libvirt and virt-manager and the UEFI files from the packages of that distro. I hope you understand that for someone who is learning there are many unknowns to solve. I hope you understand that not everyone has a clear and global vision of what to do and you can't expect to always or almost always deal with experienced people. Finally, I hope you understand that what is simple for you is not or it is less so easy for other users.
Mario.