Not saying he can't run his programs, but I have occasionally tried some programs I used when I still had Win 98 and they still work on Win 10. I think bigger problems are hardware drivers for older equipment at times.
That happens with Windows is you can have some backwards compatibility problems.
XP was a good platform.
Load a fresh copy of XP on a PC and go on the internet.
The pop-ups, spyware, and malware will have such a field day you wont be able to finish getting it set up.
All the updates are not available from MS anymore.
You can still find them from the same places that give your PC a virus.
The drivers for newer peripherals may not be available for XP.
Many things now are plug and play.
Plug it in and it loads the drivers for Win 7-10.
You have to manually load the correct drivers and disable the auto load feature.
Win 7-10 can be run as XP in an emulator.
But then nothing works in XP as you don't have the correct drivers.
Remember XP was set up to dial up to get internet.
For software pay attention to if it's a subscription or owned. If you have a copy or always need the internet to run the software (the actual software is in a cloud). I prefer it on the PC so it can work without internet for travels and is more responsive IMO. Watch out for PC's that are pre-loaded with software like MS office. Many computers are loaded with the software, but you don't own it, and it wont work. Until you log in and pay for the software. At best an ad on you computer to use a certain software, at worst deceptive marketing.
Myself I like a computer striped down as possible. Then I decide what I purchase and install on the PC.
Such as does it come with the version of Quick books you want, say Quick Books Contractor.
Or which version of MS Office do you get. Lots of versions out there with different features and user rights.
Such as do you want to use a student version for business.
Another thing to watch out for if you purchase in the store. I almost bought 1 pc that had less memory listed on the box sticker than the display model. Told em I didn't want that one. They grabbed another box, same model and upc number, with more memory.
I had a Dell laptop. Lasted 2 weeks. Dell replaced it in 2 weeks after mailing in the first. Kinda plasticy IMO.
Also had an HP, but it was so long ago you can't compare cause that thing was made out of stone.