He influenced many people, both directly and indirectly, but had a...difficult personality. He has many thousands of pages of written work, but resisted finalizing anything "publishable". His style is (IMO) an extreme example of that dense, meandering, 19th-century Victorian style, which can make for very hard reading.
But he made significant contributions to many fields, from mathematics to experimental physics to logic to (nascent) computer science to philosophy.
This 2019 article from Aeon magazine outlines much of it: The American Aristotle https://aeon.co/essays/charles-sanders-peirce-was-americas-g...
Umberto Eco said: "Charles Sanders Peirce is undoubtedly the greatest unpublished writer of our century." (cf. https://www.jstor.org/stable/2907146)
Cornel West said: "Charles Sanders Peirce is the most profound philosophical thinker produced in America."
For example, Peirce coined the term "fallibilism":
> For years in the course of this ripening process, I used for myself to collect my ideas under the designation fallibilism; and indeed the first step toward finding out is to acknowledge you do not satisfactorily know already; so that no blight can so surely arrest all intellectual growth as the blight of cocksureness; and ninety-nine out of every hundred good heads are reduced to impotence by that malady — of whose inroads they are most strangely unaware! Collected Papers, §1.13
He was the first to articulate the type/token distinction. He has truth tables ~40 years before Wittgenstein. He had diagrams of electrical circuits that could do basic logic. He was the first to show (in the 1880s) that NOR and NAND were sufficient to reproduce the other logical connectives.
He was the first to propose tying a standard unit to an absolute measure (in Peirce's case, defining the meter in terms of the wavelength of a spectral line): https://pubs.aip.org/physicstoday/article/62/12/39/390647/Ch...
The ideas in the paper where he proposed that were taken up by Michelson and Morley, who credit Peirce in several of their interferometer papers.