No, this is simply not true. False information was spread through social media. Tik Tok made yet another ridiculous thing go viral. Pregnancy tests simply measure the hormonal level of a woman. It detects HCG levels. HCG is a hormone that is produced heavily after a woman becomes pregnant. Cleveland Clinic wrote an article talking about the things that a test does.
Also think about this from a marketing side. A pregnancy test taken by a newly pregnant woman would read that she was pregnant. If there was a plan B inside the test, the pill would work causing the woman to no longer be pregnant. This would give the conclusion of a false positive. Now the product of the company is not reliable and people use other products. I do not see the reasoning behind a company making this real.
https://my.clevelandclinic.org/health/articles/9703-pregnancy-tests