Can I use Windows 7 or Windows 8 on the HP ProBook 450 G5?

No, HP does not support Windows 8 or Windows 7 on products configured with Intel 7th Generation and forward processors, in accordance with Microsoft's support policy. HP also does not provide Windows 7 or Windows 8 drivers for these configurations on the HP support website. The recommended operating system is Windows 10 Pro. (Page 4)