Play the class you want
I was in a similar situation, wanting to play an artificer but not knowing if it would be too hard, as someone who has played barely any 5e. Complexity-wise, I would place it as being harder than playing most martial builds, but less complicated than many full spell casters. But — with the right supports — it definitely is manageable, even with little to no DnD experience. And it's more fun than playing something you're not passionate about.
Building an Artificer
Your friend has a character concept already and that makes some choices for them. When I built my character, I didn't have a concept, and mostly used the RPGBot Guide for the class to guide my decisions. This helps cut down on a lot of options (especially bad ones!). Starting at a low level also helps new players, because it's more opportunity to play to learn what works and what doesn't before making a lot of character creation choices or having too many options when in combat.
Spells and Infusions
The main complexities in the class are that it gets both infusions and spells. However, a low level artificer will only have two infusions they can use at once, and only a few spells. The infusions that I used didn't add much complexity to combat. Many infusions increase AC (along with some situational benefit), which is not much more complicated than having a shield. The other infusion I used was on my weapon, Returning Weapon, which I didn't have to think about any more than a regular ranged weapon.
Spells prepared and infusions used can be swapped on a long rest and one infusion known can be swapped on a level up (making it not too punishing if you make mistakes with either). When I played, I kept the same infusions and mostly the same spells each day, which made things drastically simpler.
In addition to that, many artificers will control a "pet". At the beginning that would only be a Steel Defender or a Cannon, though any wealthy artificer can have a Homunculus Servant (though it may be a good suggestion for a new player to not take that infusion). Having a pet adds some complexity, but, in my experience with the Steel Defender, it doesn't add much complexity as it has so few options of its own: it only moves, attacks, and reacts to attacks.
The Role of the Rest of the Party
You, and the other players, can also help ease a new player into their role in the party, such as by giving suggestions, reminders, and reassurance when playing. For example:
- Suggesting a healing spell on a character one hit away from falling (worrying about others' health will slow your artificer down)
- Discussing tactics briefly as a group, such as to decide who's fighting what enemies and how. (This is broadly applicable to many character builds, but especially so for the artificer, who can do many things in combat: ranged attack, melee attack, spell attack, be a tank, distract, heal or give other spell support. Knowing what your doing on your turn in advanced makes it much easier.)
- Reminding about Guidance before making a skill check (I wasn't looking at my character sheet out of combat, so it was easy to forget about options like these)