No. A website cannot access your SEID unless you explicitly install a configuration profile or grant an enterprise app the “NFC & Payment” entitlement.
There is no official "SEID check link" provided by Apple to verify your device's security or status. If you are looking to find your SEID (Secure Element ID)—a unique identifier for the hardware security chip used for Apple Pay and NFC—you can find it directly on your device. How to Find Your SEID Number seid iphone check link
SEID stands for Secure Element Identifier. It is a unique, permanent 32-character hexadecimal string embedded in the Secure Element chip of your iPhone. The Secure Element is a dedicated hardware component that stores sensitive data like Apple Pay card tokens, transit passes, and access credentials. For Checking Linked Devices on iCloud
Is SEID the same as IMEI or serial number? Go to iCloud