Do platforms really know you're using a datacenter proxy?

Yes. Most platforms can easily see when ur using a proxy / vpn . what matters the most is the quality in order to ensure site functionability.

Even if your TLS fingerprint is perfectly spoofed using uTLS, platforms cross reference your IP's ASN. Datacenter IP blocks are publicly registered and hard-flagged in fraud databases. If a request claims to be a normal mobile user but originates from an AWS or commercial hosting ASN, it’s an automatic drop. The only way around network level detection at scale is routing through, physical mobile carrier ASNs like O2 or EE.