Does anyone know what to fill in for Payer’s TIN in 1099 NEC where the format is a social security number but the tax info only provides the last 4 digits?

You don't need to enter that.  I would forget about entering the 1099NEC or 1099Misc. Just enter the total as Other self employment income or as Cash or General income. You don't need to enter each 1099NEC or 1099K. You can enter all your income as Cash. Only the total goes to schedule C.

How to enter income from Self Employment
https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/26653