What do you use as a response rate benchmark?

Try to achieve 100%.
Failing that means that the survey responses that you get are about a subpopulation that responds to surveys. The response from this population may be different from the entire population. Depending on the goals, you might need to look into assessing if your responses are not an accurate representation of the total population. There can be other issues like some portion of the surveyed population finds your questions (or at least one question) offensive.
A different approach would be to ask if there were enough favorable responses to enable your product to be successful despite other factors. At least in the political arena, some "surveys" seem to be more advertisement than data gathering tools.

I would say it differs from sector to sector, depending on what your business is. If you're a shoes chain in South America, your response targets are going to look vastly differently from a healthcare technology company in the UK.
My company is an association of children's hospitals based out of North America, so our targets are based on similar surveys whose target demographic is all hospitals, not just limited to children's hospitals. See if you can find a survey for a company in your genre and get an idea of a better benchmark from them/their published data set.

A little late to the party, but 100% response rate is totally unrealistic.
Statistically, you should focus on reaching a representativeness, confidence level and margin of error that make sense for you. Usually we aim at 95% confidence level with 5% margin of error, but some may be flexible to 7 or 8% margin of error if they are working with smaller samples. There are plenty of calculator only to help you figure out your targeted number of respondents.
Also, Qualtrics offer a library of NPS and average benchmarks so you can compare with industries similar to yours that could provide a more in-depth on your results.