How do I enter a 1099R for a Pension, not a 401K or Roth?

You only need to enter the Form 1099-R as received.  If you are age 72 or older you will be asked if this distribution was an RMD.  Since it is pension income, Answer Yes, it is all an RMD.

To enter, edit or delete a form 1099-R -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On IRA, 401(k), Pension Plan Withdrawals (1099-R), click the start or update button

Or enter 1099-r in the Search box located in the upper right of the program screen. Click on Jump to 1099-R

On the screen Did you get a 1099-R in 2023? Click on Yes

On the next screen click on Continue

On the screen Let's import your tax info Click on Change how I enter my form

On the screen How do you want to add your 1099‑R? Click on Type it in myself

On the screen Who gave you a 1099-R? select the type of 1099-R you received and Continue