Am I considered a Full-time student for the year 2021?

You do not need to be a fulltime student to claim a tuition credit.  Half time or more qualifies. 

The full time student for 5 months rule comes into play for determining dependent status. 

There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test.

A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:

1. He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
2. He did not provide more than 1/2 his own support. Scholarships are excluded from the support calculation
3. He lived with the parent (including temporary absences such as away at school) for more than half the year

Full time student status, for parts of 5 calendar months, prevents you from claiming the Retirement Savers Credit.