My guess, they where older Sammies?
If so, please state TV model and Plex Client used, and when said, then do note the following:
- Due to the world been a sometime nasty place, where hackers etc. lives, Plex has to upgrade their WebSite security in order to protect us all!
- As such, Plex upgraded their websites to use newer encryption, as well as chipers. (Ref: Plex support is ending 2020-09-30 on older smart TV devices)
- And if they didn’t do that, everybody would be in the risk of been comprimised
- This sadly means, that if a TV vendor hasn’t updated their OS to support newer encryption or chipers, the TV can’t connect to a WebSite, that has (And should have) their security updated
- Sadly, I have +3 Sammies E-Series (2012) that by Sammy is deemed EOL, so they have not been updated by Samsung.
- This could be both due to a Samsung policy, or due to HW in the TV can’t handle it, so I’ll refrain from judging here
For Samsung E-Series, their supported Chipers, are sadly more or less unsecure 
/* RSA with NULL cipher and MD5 MAC
* for test purposes.
*/
#define GNUTLS_RSA_NULL_MD5 { 0x00, 0x01 }
#define GNUTLS_RSA_NULL_SHA1 { 0x00, 0x02 }
#define GNUTLS_RSA_NULL_SHA256 { 0x00, 0x3B }
/* ANONymous cipher suites.
*/
#define GNUTLS_ANON_DH_3DES_EDE_CBC_SHA1 { 0x00, 0x1B }
#define GNUTLS_ANON_DH_ARCFOUR_MD5 { 0x00, 0x18 }
/* rfc3268: */
#define GNUTLS_ANON_DH_AES_128_CBC_SHA1 { 0x00, 0x34 }
#define GNUTLS_ANON_DH_AES_256_CBC_SHA1 { 0x00, 0x3A }
/* rfc4132 */
#ifdef ENABLE_CAMELLIA
#define GNUTLS_ANON_DH_CAMELLIA_128_CBC_SHA1 { 0x00,0x46 }
#define GNUTLS_ANON_DH_CAMELLIA_256_CBC_SHA1 { 0x00,0x89 }
#endif
#define GNUTLS_ANON_DH_AES_128_CBC_SHA256 { 0x00, 0x6C }
#define GNUTLS_ANON_DH_AES_256_CBC_SHA256 { 0x00, 0x6D }
/* PSK (not in TLS 1.0)
* draft-ietf-tls-psk:
*/
#define GNUTLS_PSK_SHA_ARCFOUR_SHA1 { 0x00, 0x8A }
#define GNUTLS_PSK_SHA_3DES_EDE_CBC_SHA1 { 0x00, 0x8B }
#define GNUTLS_PSK_SHA_AES_128_CBC_SHA1 { 0x00, 0x8C }
#define GNUTLS_PSK_SHA_AES_256_CBC_SHA1 { 0x00, 0x8D }
#define GNUTLS_DHE_PSK_SHA_ARCFOUR_SHA1 { 0x00, 0x8E }
#define GNUTLS_DHE_PSK_SHA_3DES_EDE_CBC_SHA1 { 0x00, 0x8F }
#define GNUTLS_DHE_PSK_SHA_AES_128_CBC_SHA1 { 0x00, 0x90 }
#define GNUTLS_DHE_PSK_SHA_AES_256_CBC_SHA1 { 0x00, 0x91 }
/* SRP (rfc5054)
*/
#define GNUTLS_SRP_SHA_3DES_EDE_CBC_SHA1 { 0xC0, 0x1A }
#define GNUTLS_SRP_SHA_RSA_3DES_EDE_CBC_SHA1 { 0xC0, 0x1B }
#define GNUTLS_SRP_SHA_DSS_3DES_EDE_CBC_SHA1 { 0xC0, 0x1C }
#define GNUTLS_SRP_SHA_AES_128_CBC_SHA1 { 0xC0, 0x1D }
#define GNUTLS_SRP_SHA_RSA_AES_128_CBC_SHA1 { 0xC0, 0x1E }
#define GNUTLS_SRP_SHA_DSS_AES_128_CBC_SHA1 { 0xC0, 0x1F }
#define GNUTLS_SRP_SHA_AES_256_CBC_SHA1 { 0xC0, 0x20 }
#define GNUTLS_SRP_SHA_RSA_AES_256_CBC_SHA1 { 0xC0, 0x21 }
#define GNUTLS_SRP_SHA_DSS_AES_256_CBC_SHA1 { 0xC0, 0x22 }
/* RSA
*/
#define GNUTLS_RSA_ARCFOUR_SHA1 { 0x00, 0x05 }
#define GNUTLS_RSA_ARCFOUR_MD5 { 0x00, 0x04 }
#define GNUTLS_RSA_3DES_EDE_CBC_SHA1 { 0x00, 0x0A }
#define GNUTLS_RSA_EXPORT_ARCFOUR_40_MD5 { 0x00, 0x03 }
/* rfc3268:
*/
#define GNUTLS_RSA_AES_128_CBC_SHA1 { 0x00, 0x2F }
#define GNUTLS_RSA_AES_256_CBC_SHA1 { 0x00, 0x35 }
/* rfc4132 */
#ifdef ENABLE_CAMELLIA
#define GNUTLS_RSA_CAMELLIA_128_CBC_SHA1 { 0x00,0x41 }
#define GNUTLS_RSA_CAMELLIA_256_CBC_SHA1 { 0x00,0x84 }
#endif
#define GNUTLS_RSA_AES_128_CBC_SHA256 { 0x00, 0x3C }
#define GNUTLS_RSA_AES_256_CBC_SHA256 { 0x00, 0x3D }
/* DHE DSS
*/
#define GNUTLS_DHE_DSS_3DES_EDE_CBC_SHA1 { 0x00, 0x13 }
/* draft-ietf-tls-56-bit-ciphersuites-01:
*/
#define GNUTLS_DHE_DSS_ARCFOUR_SHA1 { 0x00, 0x66 }
/* rfc3268:
*/
#define GNUTLS_DHE_DSS_AES_256_CBC_SHA1 { 0x00, 0x38 }
#define GNUTLS_DHE_DSS_AES_128_CBC_SHA1 { 0x00, 0x32 }
/* rfc4132 */
#ifdef ENABLE_CAMELLIA
#define GNUTLS_DHE_DSS_CAMELLIA_128_CBC_SHA1 { 0x00,0x44 }
#define GNUTLS_DHE_DSS_CAMELLIA_256_CBC_SHA1 { 0x00,0x87 }
#endif
#define GNUTLS_DHE_DSS_AES_128_CBC_SHA256 { 0x00, 0x40 }
#define GNUTLS_DHE_DSS_AES_256_CBC_SHA256 { 0x00, 0x6A }
/* DHE RSA
*/
#define GNUTLS_DHE_RSA_3DES_EDE_CBC_SHA1 { 0x00, 0x16 }
/* rfc3268:
*/
#define GNUTLS_DHE_RSA_AES_128_CBC_SHA1 { 0x00, 0x33 }
#define GNUTLS_DHE_RSA_AES_256_CBC_SHA1 { 0x00, 0x39 }
/* rfc4132 */
#ifdef ENABLE_CAMELLIA
#define GNUTLS_DHE_RSA_CAMELLIA_128_CBC_SHA1 { 0x00,0x45 }
#define GNUTLS_DHE_RSA_CAMELLIA_256_CBC_SHA1 { 0x00,0x88 }
#endif
#define GNUTLS_DHE_RSA_AES_128_CBC_SHA256 { 0x00, 0x67 }
#define GNUTLS_DHE_RSA_AES_256_CBC_SHA256 { 0x00, 0x6B }
/* Safe renegotiation */
#define CIPHER_SUITES_COUNT sizeof(cs_algorithms)/sizeof(gnutls_cipher_suite_entry)-1
So in short…
A Smart-TV is a computer, and my TV from 2012 is a very old computer, so I sadly have to figure out new ways here, since I naturally doesn’t expect Plex to downgrade => compromise us all
So I’ll be looking for a thing like a shield, Apple-TV or a Chromecast
