xbuild.exe: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/mono/xbuild/12.0/bin/xbuild.exe - from package: mono-xbuild

You may install the required package with command apt-get install {package}

Error in other languages:
xbuild.exe: bevel nie gevind nie
xbuild.exe: comandă negăsită
xbuild.exe: comando não encontrado
xbuild.exe: commande introuvable
xbuild.exe: command not found
xbuild.exe: käsku ei ole
xbuild.exe: không tìm thấy lệnh
xbuild.exe: komanda nerasta
xbuild.exe: Kommando nicht gefunden.
xbuild.exe: kommandot finns inte
xbuild.exe: komut yok
xbuild.exe: nie znaleziono polecenia
xbuild.exe: níor aimsíodh an t-ordú
xbuild.exe: no se encontró la orden
xbuild.exe: no s'ha trobat l'ordre
xbuild.exe: opdracht niet gevonden
xbuild.exe: parancs nem található
xbuild.exe: perintah tidak ditemukan
xbuild.exe: príkaz nenájdený
xbuild.exe: příkaz nenalezen
xbuild.exe: команда не найдена
xbuild.exe: командата не е открита
xbuild.exe: 命令找不到
xbuild.exe: コマンドが見つかりません