Hello Robert,

thanks a lot for the prompt reply! Adding 'CONFIG_NET_SOCKETS_OFFLOAD=n' did the trick and have managed to connect 🎉

...
*** Booting Zephyr OS build zephyr-v3.2.0-3154-g3c4783042eed ***
[00:00:00.545,000] <dbg> net_lwm2m_engine: lwm2m_engine_init: LWM2M engine socket receive thread started
[00:00:00.546,000] <dbg> net_lwm2m_obj_security: security_create: Create LWM2M security instance: 0
[00:00:00.546,000] <dbg> net_lwm2m_obj_server: server_create: Create LWM2M server instance: 0
[00:00:00.546,000] <dbg> net_lwm2m_obj_device: device_create: Create LWM2M device instance: 0
[00:00:00.546,000] <dbg> net_lwm2m_obj_firmware: firmware_create: Create LWM2M firmware instance: 0
[00:00:00.546,000] <inf> net_lwm2m_client_app: Initializing network connection...
Connected
[00:00:05.522,000] <inf> net_lwm2m_client_app: Connected to network
[00:00:05.522,000] <inf> net_lwm2m_client_app: Your address: 192.168.1.43
[00:00:05.522,000] <inf> net_lwm2m_client_app: Lease time: 0 seconds
[00:00:05.522,000] <inf> net_lwm2m_client_app: Subnet: 0.0.0.0
[00:00:05.522,000] <inf> net_lwm2m_client_app: Router: 0.0.0.0
[00:00:05.522,000] <inf> net_lwm2m_client_app: Run LWM2M client
[00:00:05.522,000] <dbg> net_lwm2m_registry: lwm2m_engine_set: path:0/0/2, value:0x2000d497, len:1
[00:00:05.522,000] <dbg> net_lwm2m_registry: lwm2m_engine_set: path:0/0/10, value:0x2000d496, len:2
[00:00:05.522,000] <dbg> net_lwm2m_registry: lwm2m_engine_set: path:1/0/0, value:0x2000d496, len:2
[00:00:05.525,000] <dbg> net_lwm2m_registry: lwm2m_engine_create_obj_inst: path:3303/0
[00:00:05.525,000] <dbg> net_ipso_temp_sensor: temp_sensor_create: Create IPSO Temperature Sensor instance: 0
[00:00:05.525,000] <dbg> net_lwm2m_registry: lwm2m_engine_create_obj_inst: path:3311/0
[00:00:05.525,000] <dbg> net_ipso_light_control: light_control_create: Create IPSO Light Control instance: 0
[00:00:05.525,000] <dbg> net_lwm2m_registry: lwm2m_engine_create_obj_inst: path:3340/0
[00:00:05.525,000] <dbg> net_ipso_timer: timer_inst_create: Create IPSO Timer instance: 0
[00:00:05.525,000] <inf> net_lwm2m_rd_client: Start LWM2M Client: disco_l475_iot1
[00:00:05.525,000] <dbg> net_lwm2m_registry: lwm2m_engine_set: path:3303/0/5700, value:0x2000d8f0, len:8
[00:00:06.047,000] <dbg> net_lwm2m_registry: lwm2m_engine_get: path:0/0/1, buf:0x2000bfa7, buflen:1
[00:00:06.047,000] <dbg> net_lwm2m_registry: lwm2m_engine_get: path:0/0/10, buf:0x2000bfde, buflen:2
[00:00:06.047,000] <dbg> net_lwm2m_registry: lwm2m_engine_get: path:1/0/1, buf:0x2000bfb0, buflen:4
[00:00:06.047,000] <inf> net_lwm2m_rd_client: RD Client started with endpoint 'disco_l475_iot1' with client lifetime 30
[00:00:06.047,000] <dbg> net_lwm2m_message_handling: lwm2m_parse_peerinfo: Parse url: coap://192.168.1.28
[00:00:06.162,000] <inf> net_lwm2m_engine: Connected, sock id 0
[00:00:06.162,000] <dbg> net_lwm2m_registry: lwm2m_engine_get: path:1/0/1, buf:0x2000bf60, buflen:4
[00:00:06.163,000] <dbg> net_lwm2m_rd_client: sm_send_registration: registration sent [192.168.1.28]
[00:00:06.612,000] <dbg> net_lwm2m_message_handling: lwm2m_udp_receive: checking for reply from [192.168.1.28]
[00:00:06.612,000] <dbg> net_lwm2m_rd_client: do_registration_reply_cb: Registration callback (code:2.1)
[00:00:06.612,000] <dbg> net_lwm2m_client_app: rd_client_event: Registration complete
[00:00:06.612,000] <inf> net_lwm2m_rd_client: Registration Done (EP='pNA7MXGawK')
[00:00:06.613,000] <dbg> net_lwm2m_message_handling: lwm2m_udp_receive: reply 0x20004dbc handled and removed
[00:00:06.660,000] <dbg> net_lwm2m_message_handling: lwm2m_udp_receive: checking for reply from [192.168.1.28]
[00:00:06.660,000] <dbg> net_lwm2m_message_handling: lwm2m_engine_default_content_format: No accept option given. Assume SenML CBOR.
[00:00:06.660,000] <dbg> net_lwm2m_observation: engine_observe_node_init: OBSERVER ADDED 3303/0/5700/0(3)
[00:00:06.660,000] <inf> net_lwm2m_client_app: Observer added for 3303/0/5700
[00:00:06.660,000] <dbg> net_lwm2m_observation: engine_observe_node_init: token:'55624fcb7537c1ea' addr:192.168.1.28
[00:00:31.556,000] <dbg> net_lwm2m_registry: lwm2m_engine_get: path:1/0/1, buf:0x2000bf70, buflen:4
[00:00:31.556,000] <dbg> net_lwm2m_rd_client: sm_send_registration: registration sent [192.168.1.28]
[00:00:31.752,000] <dbg> net_lwm2m_message_handling: lwm2m_udp_receive: checking for reply from [192.168.1.28]
[00:00:31.752,000] <inf> net_lwm2m_rd_client: Update callback (code:2.4)
[00:00:31.752,000] <dbg> net_lwm2m_client_app: rd_client_event: Registration update complete
[00:00:31.752,000] <inf> net_lwm2m_rd_client: Update Done
...

Thanks a lot! 🙏

Kind regards,
-Christos