@NCperson
The rules for the dependent care credit for “full-time student“ are not the same as for educational benefits or the definition of dependent. The nonworking spouse is only eligible for the credit during the months when they are actually a full-time student. If the nonworking spouse was a full-time student in five months, they may qualify for certain educational credits, but they do not qualify for the dependent care credit for the entire year, only the five months in which they were a full-time student.
For example, if there is one child in care and using the 2022 limits, the maximum credit is applied toward $3000 of expenses. The maximum expenses that can be claimed is either $3000, or the income of the lowest earning spouse, whichever is lower. The nonworking spouse is allocated $250 of income for each month that they are a student, for purpose of calculating the credit. If the nonworking spouse was a student for five months, and had no income for the rest of the year, they could claim a maximum of $1250 of care expenses toward the credit. On the other hand, because of the way form 2441 works, if the nonworking spouse had a job and earned $3000 in one month, and was unemployed or a student for the rest of the year, they would qualify for the maximum credit because their earnings for the year were at least $3000, even if they were earned all in one month. (This is not necessarily how the credit was intended to be used but it is how the forms and instructions actually work.)
