For the Magus, Spell Swipe (and eventually Whirlwind Spell) allows you to hit multiple enemies with a Spellstrike; however, if you actually want your multiple targets to both get hit by a spell, you need a spell that can target multiple creatures with a Spell Attack roll*:
If your spell could affect two or more targets, your spell affects whichever foes you hit, not just the first target; otherwise, choose one target to affect with the spell.
The only spell I'm aware of that targets multiple creatures with a Spell Attack roll is Scorching Ray. Are there any other spells that could work with this? Preferably also not focus spells that I'd have to take a dedication to get to (i.e. Magus focus spells are fine, but Domain focus spells not so much).
*I'm aware Expansive Spellstrike increases the options (adding, importantly, Electric Arc and Scatter Scree), but I'm hoping to take a different feat at level 2 and don't want to have to make room for it in my build.
Best Answer
There is currently no other* multiple attack Arcane spell
*Not counting Horizon Thunder Sphere's AoE because it's not valid with Spellstrike
I couldn't think of a good way to parse this, but realized a relatively simple way: the Spells section of the [Attack] trait has what should be a full list of spells, which is fairly limited (for now) that involve attack rolls. Going through them, the ones typically available in Arcane are: