EMQX 5.8.4 (Open Source) fresh install
MQTT default settings

Authentication
Built-in Database Password-Based
UserID Type: username
Password Hash: plain

User Management
Username: admin
Password: public

Authorization
File disabled

Built-in Database Permissions
Username: admin
Action: Publish & Subscribe
Permission: Allow
Topic: test

Gateway CoAP
default settings
Connection Required: false

Authentication Built-in Database
UserID Type: username
Password Hash: plain

User Management
username: admin
password: public

Test 1
root@mail:~# coap-client -m post -e "" "coap://127.0.0.1/mqtt/connection?clientid=123&u=admin&p=public"
2427013631
root@mail:~# coap-client -m post -e "Hi, Connection Mode" "coap://127.0.0.1/ps/test/topic?&c=123&t=2427013631"
root@mail:~#

root@mail:~# mqttx sub -h 127.0.0.1 -p 1883 -i sub -t test/topic -u 'admin' -P 'public'
✔ Connected
✔ Subscribed to test/topic
topic: test/topic, qos: 0
Hi, Connection Mode

----------------------------
Test is good
----------------------------

Log
2025-01-21T18:09:33.903266+01:00 [MQTT] sub@127.0.0.1:50946 msg: mqtt_packet_received, packet: CONNECT(Q0, R0, D0, ClientId=sub, ProtoName=MQTT, ProtoVsn=5, CleanStart=true, KeepAlive=60, Username=admin, Password=******), username: admin
2025-01-21T18:09:33.903860+01:00 [AUTHN] sub@127.0.0.1:50946 msg: authenticator_result, authenticator: password_based:built_in_database, result: {ok,#{is_superuser => false}}, username: admin
2025-01-21T18:09:33.904084+01:00 [AUTHN] sub@127.0.0.1:50946 msg: authentication_result, reason: chain_result, result: {stop,{ok,#{is_superuser => false}}}, username: admin
2025-01-21T18:09:33.905615+01:00 [MQTT] sub@127.0.0.1:50946 msg: mqtt_packet_sent, packet: CONNACK(Q0, R0, D0, AckFlags=0, ReasonCode=0), username: admin
2025-01-21T18:09:33.911620+01:00 [MQTT] sub@127.0.0.1:50946 msg: mqtt_packet_received, packet: SUBSCRIBE(Q1, R0, D0, PacketId=50346 TopicFilters=[test/topic(#{nl => 0,qos => 0,rh => 0,rap => 0})]), username: admin
2025-01-21T18:09:33.911866+01:00 [AUTHZ] sub@127.0.0.1:50946 msg: authorization_module_ignore, action: SUBSCRIBE(Q0), module: emqx_authz_client_info, topic: test/topic, username: admin
2025-01-21T18:09:33.912176+01:00 [AUTHZ] sub@127.0.0.1:50946 msg: authorization_nomatch, action: SUBSCRIBE(Q0), authorize_type: built_in_database, module: emqx_authz_mnesia, topic: test/topic, username: admin
2025-01-21T18:09:33.912342+01:00 [SUBSCRIBE] sub@127.0.0.1:50946 msg: subscribe, sub_id: sub, sub_opts: [nl: 0, qos: 0, rh: 0, rap: 0, sub_props: []], topic: test/topic, username: admin
2025-01-21T18:09:33.912787+01:00 [MQTT] sub@127.0.0.1:50946 msg: mqtt_packet_sent, packet: SUBACK(Q0, R0, D0, PacketId=50346, ReasonCodes=[0]), username: admin
2025-01-21T18:09:41.856802+01:00 [AUTHN] 123@127.0.0.1:38070 msg: authenticator_result, authenticator: password_based:built_in_database, result: {ok,#{is_superuser => false}}
2025-01-21T18:09:41.857034+01:00 [AUTHN] 123@127.0.0.1:38070 msg: authentication_result, reason: chain_result, result: {stop,{ok,#{is_superuser => false}}}
2025-01-21T18:09:54.824388+01:00 [AUTHZ] @127.0.0.1:33239 msg: authorization_module_ignore, action: PUBLISH(Q1,R0), module: emqx_authz_client_info, topic: test/topic, username: undefined
2025-01-21T18:09:54.824970+01:00 [AUTHZ] @127.0.0.1:33239 msg: authorization_nomatch, action: PUBLISH(Q1,R0), authorize_type: built_in_database, module: emqx_authz_mnesia, topic: test/topic, username: undefined
2025-01-21T18:09:54.825761+01:00 [PUBLISH] @127.0.0.1:33239 msg: publish_to, payload_encode: text, topic: test/topic, payload: Hi, Connection Mode
2025-01-21T18:09:54.827286+01:00 [MQTT] sub@127.0.0.1:50946 msg: mqtt_packet_sent, packet: PUBLISH(Q0, R0, D0, Topic=test/topic, PacketId=undefined, Payload(text)=Hi, Connection Mode), username: admin

-----------------------------------

Changing Gateway CoAP
default settings
Connection Required: true

Test 2
root@mail:~# coap-client -m post -e "" "coap://127.0.0.1/mqtt/connection?clientid=123&u=admin&p=public"
925055100
root@mail:~# coap-client -m post -e "Hi, Connection Mode" "coap://127.0.0.1/ps/test/topic?&c=123&t=925055100"
925055100
root@mail:~# coap-client -m post -e "Hi, Connection Mode" "coap://127.0.0.1/ps/test/topic?&c=123&t=925055100"
925055100
root@mail:~#

root@mail:~# mqttx sub -h 127.0.0.1 -p 1883 -i sub -t test/topic -u 'admin' -P 'public'
✔ Connected
✔ Subscribed to test/topic

----------------------------
Test fail do not receive the topic in mqttx
----------------------------

Log
2025-01-21T18:18:05.040731+01:00 [MQTT] sub@127.0.0.1:53876 msg: mqtt_packet_received, packet: CONNECT(Q0, R0, D0, ClientId=sub, ProtoName=MQTT, ProtoVsn=5, CleanStart=true, KeepAlive=60, Username=admin, Password=******), username: admin
2025-01-21T18:18:05.041074+01:00 [AUTHN] sub@127.0.0.1:53876 msg: authenticator_result, authenticator: password_based:built_in_database, result: {ok,#{is_superuser => false}}, username: admin
2025-01-21T18:18:05.041211+01:00 [AUTHN] sub@127.0.0.1:53876 msg: authentication_result, reason: chain_result, result: {stop,{ok,#{is_superuser => false}}}, username: admin
2025-01-21T18:18:05.042361+01:00 [MQTT] sub@127.0.0.1:53876 msg: mqtt_packet_sent, packet: CONNACK(Q0, R0, D0, AckFlags=0, ReasonCode=0), username: admin
2025-01-21T18:18:05.047618+01:00 [MQTT] sub@127.0.0.1:53876 msg: mqtt_packet_received, packet: SUBSCRIBE(Q1, R0, D0, PacketId=3956 TopicFilters=[test/topic(#{nl => 0,qos => 0,rh => 0,rap => 0})]), username: admin
2025-01-21T18:18:05.047819+01:00 [AUTHZ] sub@127.0.0.1:53876 msg: authorization_module_ignore, action: SUBSCRIBE(Q0), module: emqx_authz_client_info, topic: test/topic, username: admin
2025-01-21T18:18:05.048045+01:00 [AUTHZ] sub@127.0.0.1:53876 msg: authorization_nomatch, action: SUBSCRIBE(Q0), authorize_type: built_in_database, module: emqx_authz_mnesia, topic: test/topic, username: admin
2025-01-21T18:18:05.048174+01:00 [SUBSCRIBE] sub@127.0.0.1:53876 msg: subscribe, sub_id: sub, sub_opts: [nl: 0, qos: 0, rh: 0, rap: 0, sub_props: []], topic: test/topic, username: admin
2025-01-21T18:18:05.048490+01:00 [MQTT] sub@127.0.0.1:53876 msg: mqtt_packet_sent, packet: SUBACK(Q0, R0, D0, PacketId=3956, ReasonCodes=[0]), username: admin
2025-01-21T18:18:13.485756+01:00 [AUTHN] 123@127.0.0.1:51439 msg: authenticator_result, authenticator: password_based:built_in_database, result: {ok,#{is_superuser => false}}
2025-01-21T18:18:13.486348+01:00 [AUTHN] 123@127.0.0.1:51439 msg: authentication_result, reason: chain_result, result: {stop,{ok,#{is_superuser => false}}}
2025-01-21T18:19:05.065325+01:00 [MQTT] sub@127.0.0.1:53876 msg: mqtt_packet_received, packet: PINGREQ(Q0, R0, D0), username: admin
2025-01-21T18:19:05.066186+01:00 [MQTT] sub@127.0.0.1:53876 msg: mqtt_packet_sent, packet: PINGRESP(Q0, R0, D0), username: admin