15 to 20 years ago, the aerospace company I worked at had been able to defend itself in an intellectual property infringement lawsuit, though just barely as I seem to recall.
Part of the defense against such lawsuits is to maintain a real-time history of the development of a design in the form of design notes that can be properly dated. As I recall, we were able to provide those but just because that individual engineer kept his lab notes that way.
As a result, all engineers were given special notebooks in which we were to keep the same kind of dated and detailed design notes. Since I was a software engineer, my code was self-documenting (along with the version histories in our source repository).
So if someone would want to sue you for stealing their idea, they would need to show some record of having come up with that idea before you did. And since it is possible for a number of people to come up with the same idea independently* he would also need to show that you had gotten your idea from him, though I cannot think how.
My ex-wife had come up with ideas for books or movies, but which she never shared, that years later were made by somebody else (eg, "Escape from New York") and I have come up with a few technical ideas myself which I never shared and which later appeared as products. Great minds think alike. A time-travel agency sci-fi book series (Agent of T.E.R.R.A., guess when that was published) even went into several instances of key inventions (eg, calculus) being developed by several people independently such that if the one who got the credit had been killed that invention would still have made with someone else getting the credit.
Does anyone recall the scandalous voter fraud that Sidney Powell discovered in Edison County, MI? But it turns out that there is no such county! (eg, Election lawsuit cites fraud in Michigan county that does not exist, Detroit Free Press, 01 Dec 2020) . That one was almost as schadenfreudilicious as the charges of fraud in the Wisconsin election taking place in the election center in Detroit (which is in Michigan, not Wisconsin).
At that time, I looked up Edison County in Wikipedia and it redirected me to the Fictitious entry article. There's a common practice in publishing public information to prevent someone else plagiarizing your work, or at least to be able to prove in a lawsuit that they had indeed stolen your work.
That practice is to insert false entries. False names and phone numbers in a phone book. False words in a dictionary. False locations in a map or atlas. Deliberately misspelled words in specific places in pages of text. IOW, inject errors. If any of those errors also show up in the plagiarizer's publication, then that's proof that they copied it from you. I first heard of this practice over two decades ago when NCSE Reports published an article on pseudogenes caused by mechanisms such as Endogenous retrovirus (ERVs), the patterns of which can be used to show common inheritance and relatedness between species.
Edited by dwise1, : ABE, also "So if someone would want to ... "