hello_mqtt is just the context store variable name.
here is a funcntion and change node that do the exact same thing
[{"id":"19eb38d0.8f604f","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"device-ID/hello","payload":"{ \"dateTime\": \"2022-06-14 11:31:36\", \"runningSince\": \"2022-06-14 11:13:59\", \"deviceType\": \"BIOREACTOR\", \"deviceName\": \"BIOREACT-CC83\", \"ip\": \"192.168.1.146\" }","payloadType":"json","x":190,"y":2040,"wires":[["d97c8291.c0987"]]},{"id":"d97c8291.c0987","type":"function","z":"bf9e1e33.030598","name":"","func":"const varName = 'deviceList';\n\nlet devices = global.get(varName) || [];\n\nif (msg.payload.deviceName) {\n const dev = msg.payload.deviceName;\n const devId = dev.slice(-4);\n\n \n if (!(devices.find(obj => obj[dev] === devId))) {\n devices.push({[dev]:devId})\n global.set(varName, devices);\n }\n \n}\n\n\nmsg.options = devices; // Not working either.\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":360,"y":2100,"wires":[["5c45cfe5.8c7838"]]},{"id":"7c5a92bc.37419c","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"device-ID/hello","payload":"{\"dateTime\":\"2022-06-14 11:31:36\",\"runningSince\":\"2022-06-14 11:13:59\",\"deviceType\":\"BIOREACTOR\",\"deviceName\":\"BIOREACT-CC99\",\"ip\":\"192.168.1.146\"}","payloadType":"json","x":190,"y":2080,"wires":[["d97c8291.c0987"]]},{"id":"5c45cfe5.8c7838","type":"debug","z":"bf9e1e33.030598","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":580,"y":2220,"wires":[]},{"id":"322498fb.179d68","type":"change","z":"bf9e1e33.030598","name":"","rules":[{"t":"set","p":"deviceList","pt":"global","to":"$append(\t [$globalContext(\"deviceList\")][$$.payload.deviceName != $substring($$.payload.deviceName,-4)],\t [{$$.payload.deviceName: $substring($$.payload.deviceName,-4)}]\t)\t","tot":"jsonata"},{"t":"set","p":"options","pt":"msg","to":"deviceList","tot":"global"}],"action":"","property":"","from":"","to":"","reg":false,"x":340,"y":2180,"wires":[["5c45cfe5.8c7838","c692b223.af45e"]]},{"id":"f967ae4a.d3929","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"device-ID/hello","payload":"{ \"dateTime\": \"2022-06-14 11:31:36\", \"runningSince\": \"2022-06-14 11:13:59\", \"deviceType\": \"BIOREACTOR\", \"deviceName\": \"BIOREACT-CC83\", \"ip\": \"192.168.1.146\" }","payloadType":"json","x":110,"y":2140,"wires":[["322498fb.179d68"]]},{"id":"28e1e28b.ddeb56","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"device-ID/hello","payload":"{\"dateTime\":\"2022-06-14 11:31:36\",\"runningSince\":\"2022-06-14 11:13:59\",\"deviceType\":\"BIOREACTOR\",\"deviceName\":\"BIOREACT-CC99\",\"ip\":\"192.168.1.146\"}","payloadType":"json","x":110,"y":2180,"wires":[["322498fb.179d68"]]},{"id":"c692b223.af45e","type":"ui_dropdown","z":"bf9e1e33.030598","name":"","label":"hello","tooltip":"","place":"Select option","group":"2d4fe667.28f8ba","order":9,"width":0,"height":0,"passthru":true,"multiple":false,"options":[],"payload":"","topic":"topic","topicType":"msg","className":"","x":260,"y":2240,"wires":[[]]},{"id":"7754ef38.46cf48","type":"inject","z":"bf9e1e33.030598","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":140,"y":2300,"wires":[["4322b51a.2a7b14"]]},{"id":"4322b51a.2a7b14","type":"change","z":"bf9e1e33.030598","name":"","rules":[{"t":"delete","p":"deviceList","pt":"global"}],"action":"","property":"","from":"","to":"","reg":false,"x":380,"y":2300,"wires":[[]]},{"id":"2d4fe667.28f8ba","type":"ui_group","name":"demo","tab":"1caa8458.b17814","order":1,"disp":true,"width":"12","collapse":false},{"id":"1caa8458.b17814","type":"ui_tab","name":"Demo","icon":"dashboard","order":1,"disabled":false,"hidden":false}]