Tickets are in Airport Local Times, which could cause a lot of confusion to the passengers. For example, if you're going from Mauritius to Dubai, departure time is in the local time of Mauritius and the arrival time shown will be of Dubai.
So, to make it simpler and to eliminate confusion airlines use (+1) to indicate that the arrival is in the next day based on the local time of the arrival airport.
There always is a date at the beginning of the sector row to indicate the departure date, the (+1) if available is meant to be added to that date.
A (-1) can be seen as well for some flights such as some flights from Japan to the USA where the arrival local date is actually a day before the local departure date.
“+1” means “the next day”.
For a single flight that’s quite clear.
For itineraries with multiple flights the convention is not always the same. Some will continue from the day of departure of the initial flight (and you can get things like +2, +3…), while others will just reset for each flight, which seems to be the case here: your final flight arrives on the same day it departs (which is the next day when compared to the departure of the first flight).