Adding a second installation for development

Hi, I’m looking to develop a new site for a client. They already have an outdated WordPress website on their root domain. I have access to the admin for this, so I can export all the posts and content.

The old site needs to remain live whilst I develop the new one. I’d like to build the new site on the live domain so the client can view it, in a subfolder, eg. domain.com/dev, but I’m not sure of the best way to go about it. Can I add a second installation of wordpress in a sub folder, and will it be a straightforward installation in the usual way?

I have looked through this post: https://codex.www.ads-software.com/Running_a_Development_Copy_of_WordPress but I think it’s probably overkill for what I’m needing.

Could anyone suggest the best way to go about this?

Many thanks