No need for Audacity on a Mac—way too complicated when the need is simple. GarageBand is built into the macOS and will do everything he needs and has telephone support.

Any Core Audio compliant interface will do the job. I recommend one with a balance knob between Output/Input over USB — there are about 50 or more interfaces on the market with this feature. Number of them made by Focusrite = 0.

I like the M-Audio Air 192|6 for this use. These can be found for around $100 used — including a NIB test unit that I used to write a review and haven’t touched since. Another I like is the Mackie FxPro6v3 (version 3 is important).

Although this review is aimed towards iPad compatibility, it also applies to the Mac, it contrasts two of the units I mentioned above plus another. The MOTU M4 has the balance knob I like, the reviewed M2 does not.
Review: 3 inexpensive interfaces

BIAB 2024 Audiophile Mac
24Core/60CoreGPU M2 MacStudioUltra/8TB/192GB Sequoia, M1 MBAir, 2012 MBP
Digital Performer11, LogicPro, Finale27/Dorico/Encore/SmartScorePro64/Notion6 /Overture5