I want to install a modem in my house instead of the ISP router that does everything horribly, but I can't identify which connector this is.
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Your images are of poor quality and lacking anything that could be used for comparing the scale of the connector. It would be much easier for you to perform a Google image search for
fiber connector types and compare the images with what you have.
It sure looks like a SC/APC connector (IEC 61754-4, Subscriber Connector, Standard Connector), where the green color indicates Angled Physical Contact.