To me the reallocated sectors and if it rises/increases over time would be an indication that the disk is on the way out. So in your screenshot the count is at 140, monitor it and the read error rate to see if they are increasing.
As pointed out above, smart gives an indication but I’ve always found that you will get earlier signs so pull the disk out onto a bench and test it with the manufacturers util to see what it makes of the state of the disk.