Microsoft office now office 365 is a software as a service with a monthly subscription model. All done online only through the web browser. Overall it is a highly over rated never ending money pit and a significant pain in the ass.
My suggestion is to save your brother a shit ton of money over time and remain backwards compatible with Microsoft Office suite formats. By switching to the free open source software suite used by countless enterprise businesses around the world, Libre Office.
Very easy to use if you are used to microsoft office suite as it is a drop in replacement. With free updates for life and no drains on your wallet. If he is insists on microsoft office, then no worries, he can still use it online in the web browser no worries. But this is better IMHO.
My suggestion for a desktop computer is the Thelio Spark Empowered from system76. It is a linux native desktop computer that is plenty powerful for what he needs to do and more. They have excellent customer support, solid build quality, and are an enterprise grade desktop computer that future proofs your workflow.
https://system76.com/desktops/thelio-spark-r1-n3-empowered/configure
It uses PopOS, which is an ubuntu based linux distro. Very intuitive and easy to use. Once you use it for awhile it doubles or even triples your productivity and speed by the nature of its desktop features. Such as automatic window tiling. Overall it is a very private and secure operating system. Far superior to Windows or Mac malware pretending to be operating systems.
If he wants his old windows 10 or 7 workflow, look, and feel. To avoid minimal confusion. I can get you set up with a linux distro using the cinnamon desktop environment. That we can install gracefully too using windows themes and tweaks. So he wouldnt really know the difference. I just did this for my senior citizen mom and it finally fucking worked lol.
If he wants something a little more budget friendly. I would suggest the Lenovo ThinkCentre M75s Gen 5 with a ryzen 5 or 7 pro processor 16 gb of ram with a 500gb-1tb ssd hard drive. They are good small enterprise workstation workhorses. That you can also gracefully install Linux and Libreoffice suite on. As well as keep the woefully insecure malware and unwanted advertisement operating system infamously known as windows 11. If he is a bit of a masochist who doesnt want anything, but winblows.
If you have any more questions, or need someone to help guide you and your brother on this amazing journey. I am here for you. I have decades of exeperience professionally with Linux and computers. Would love to help.