I think the second link I provided is a simple solution that requires no code (just a polling node). I tested it with one of my temperature sensors and it works as expected.
Entities have a timeSinceChangedMs attribute measured in milliseconds. If that value is greater than 86400000 (24 hours) the state has not changed in 24 hours.
So, you can poll timeSinceChangedMs at some interval (60 seconds or whatever) and check to see if that value is greater than the time you want (not changed in 24 hours = true?).
A working example. Modify the Entity Id, Update Interval, and milliseconds (If State) for your environment. You can replace the debug 1 node with your notification.
[{"id":"bddbd75a.af7608","type":"poll-state","z":"8b43de8505f17be7","name":"","server":"f3f422ce.9f2a6","version":2,"exposeToHomeAssistant":false,"haConfig":[{"property":"name","value":""},{"property":"icon","value":""}],"updateinterval":"10","updateIntervalType":"num","updateIntervalUnits":"seconds","outputinitially":false,"outputonchanged":false,"entity_id":"sensor.basement_flood_temperature","state_type":"str","halt_if":"$entity().timeSinceChangedMs > 86400000","halt_if_type":"jsonata","halt_if_compare":"jsonata","outputs":2,"x":700,"y":300,"wires":[["1df3de1bd2af0c7b"],["69fcee022f51c44b"]]},{"id":"1df3de1bd2af0c7b","type":"debug","z":"8b43de8505f17be7","name":"debug 1","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1000,"y":280,"wires":[]},{"id":"69fcee022f51c44b","type":"debug","z":"8b43de8505f17be7","name":"debug 2","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1000,"y":340,"wires":[]},{"id":"f3f422ce.9f2a6","type":"server","name":"Home Assistant","version":5,"addon":true,"rejectUnauthorizedCerts":true,"ha_boolean":"y|yes|true|on|home|open","connectionDelay":true,"cacheJson":true,"heartbeat":false,"heartbeatInterval":30,"areaSelector":"friendlyName","deviceSelector":"friendlyName","entitySelector":"friendlyName","statusSeparator":"at: ","statusYear":"hidden","statusMonth":"short","statusDay":"numeric","statusHourCycle":"h23","statusTimeFormat":"h:m","enableGlobalContextStore":true}]