If the transaction fee is too low and unfortunately the mempool congestion doesn’t reduces such that the transaction fee rate comes down to your range of fee then the transaction will be dropped. The default time is 24 days from the day you broadcasted your transaction but it varies because nodes have different mempool settings so could still have it beyond those days which extends the time for it to be dropped. Also the wallet you might be using could have an in built rebroadcasting feature which will continually rebroadcast your transaction and then stopping it from getting dropped