I recently installed Sitecore Commerce 10 on a machine that already had XC9. If you have removed XC9 and installed XC10 it should take about an hour for SIF scripts to run. I came across an issue wherein my Commerce Services App pools were getting stopped and services were returning 503 when accessed.
The Commerce 10 SIF has a new password for CSFNDRUNTIME (Yes, it’s changed for the first time since v8.
Since your machine still has the old password the app pools will not start. Real bummer! 🙂