Don't know Puerto Rico is a country. Anyway here are the countries that go through population decline.
Countries With The Biggest Population Decline
Rank Country 2020 Population Decline estimate (%)
1 Lebanon -6.68
2 Cook Islands -2.59
3 Puerto Rico -1.59
4 American Samoa -1.4
5 Saint Pierre And Miquelon -1.15
6 Lithuania -1.13
7 Latvia -1.12
8 Moldova -1.08
9 Bulgaria -0.65
10 Estonia -0.65
11 Federated States of Micronesia -0.6
12 Northern Mariana Islands -0.55
13 Croatia -0.5
14 Serbia -0.47
15 Montenegro -0.37
16 Romania -0.37
17 Virgin Islands -0.37
18 Greece -0.31
19 Armenia -0.3
20 Trinidad and Tobago -0.3
21 Hungary -0.28
22 Belarus -0.27
23 Japan -0.27
24 Portugal -0.25
25 Saint Barthelemy -0.25

https://www.worldatlas.com/articles/countries-with-the-biggest-population-decline.html

Elon Musk was right. Interesting...