Yep, if you multiclass into any class that allows you to take extra actions you can use it for a spell. In that case, both actions can be a full spell and not limited to a cantrip.

In most situations you can only cast one spell per turn, because a spell is a combat action unless stated otherwise. The exceptions are:

-1 cantrip and one bonus action spell (either by quickened spell or a spell that has a bonus action casting time) -Multiclassing into a class that allows for extra actions, which can be used to cast spells. The cantrip restriction doesnt apply to this one -Using a reaction spell on your turn

So you could get into a situation where you cast a reaction spell at the beginning of your turn, use a cantrip as your main action, use quickened spell to use a spell as a bonus action, and then use action surge to cast another spell (that doesn’t have to be a cantrip). 4 in total at a relatively low level.

Hope that helps!