As usual (2018-11-11, 2017-10-21, 2016-12-07, 2015-12-05 and 2015-01-22), the aforementioned announcement of the official non-working public holidays in Namibia, for the calendar year 2020, states that "According to the Public Holidays Act, 1990 (Act 26 of 1990) the Monday, following a Sunday which is a public holiday, shall also be a public holiday, unless the Monday is already a public holiday." and includes a list of observance days that are not public holidays (Constitution Day, Day of the African Child, Day of the Namibian Child, and United Nations Day).
The list of 2020 public holidays in Namibia could be amended later in the year, as was the case this year, when President Hage Geingob declared Wednesday, November 27, 2019, as a one-off non-working public holiday in Namibia, on account of the Presidential and National Assembly elections being held in Namibia on that date (2019-11-13).
Links and References
Below are links to the news stories referred to in the above "Namibian 2020 Public Holidays Announced" news story, as well as links to subsequents news stories which refer to the present news story.