I am asking for a friend. She is claiming a widow's benefit (over her own) - she started claiming it in Feb of 2017 which she was 61 (she turned 62 in March 2017). She is not US citizen and resides in Germany. So far so good - but there seems to be some questions about income - there seems to be a rule that she can not work more than 45 hours per month. (Which she does not) but the question is that once she reached the retirement age that whatever income she makes should not matter - she never makes more than 10 to 12,000.
What you're describing is the foreign work test (https://www.ssa.gov/OP_Home/handbook/handbook.18/handbook-1823.html), and the foreign work test only applies until a person reaches their full retirement age (FRA). Since your friend was born in 1955 her FRA for work test purposes is age 66 & 2 months, so there would be no limits on how much she could work or earn starting with May 2021.