I just asked grok. Based on info from Pew, DHS, Wikipedia, etc. here is the salient content of the response: my guess would be:
Legal immigrants: ~68 million (based on higher-end historical estimates). Illegal immigrants: ~20–30 million total entries, with maybe 10–15 million staying permanently. Adding the lower end of illegal entries (20 million) to 68 million legal immigrants gives ~88 million. Using the higher end (30 million) pushes it to ~98 million. Splitting the difference, I’d estimate around 90–95 million people have immigrated to the U.S., legally and illegally, since 1965.