Why is this year's refund 154 times larger than last year's when income, deductions, withholding, and tax bill are similar? How do I ask Turbo for an explanation?

thsince we can see your returns, the easiest thing to do is o compare your 2022 and 2023 reeturns line for line.  most likely there's a misplaced decimal point or extra digit somewhere. 

154X isn't necessarily meaningful.  (not 154%)

..$1 vs $154 is meaningless

or $1000 vs 154,000 is a problem.

Yep, double check the actual withholding numbers you've entered...do not accidentally hit commas for decimal points.

Thanks. I'll try that but the income summary looks correct except for a page I can't find again that had mysterious reductions.

Don't use the income summary as it doesn't always include everything.  It is best to compare the actual form 1040 and Schedules 1,2 and 3 for last year to this year if something has changed drastically on the return, but in your actual situation it did not.

You can also go back to your tax forms and double check your entries.  If you had a drastic change for no reason, it is likely a typo either this year or last year.

If the typo was last year, you will need to Amend Your Return for 2022 to correct the issue.