Websites like Bestapps2020.com are usually launched by browsers infected with some Potentially Unwanted Application (PUA) automatically. Like countless other pages of this type, Bestapps2020.com has no meaningful content, and its only goal is to promote other shady pages or services on the Internet. When Bestapps2020.com hijacks the Web browser of its targeted computer, it displays an error message claiming that the user needs to click on the 'Allow' button and agree with the notifications to proceed to the page's content. There are various other clickbait techniques, yet they all rely on social engineering.
As you can already imagine, the only effect of clicking on the button is that the website receives permission to deliver advertising content to the user's desktop directly. There are many problems with that. Banners and advertisements generated by Bestapps2020.com often contain links to potentially unsafe websites or simply present deceptive offers and fake promotions, which are utterly useless for the viewer. Also, the amount of these pop-ups is such that it can even slow down the affected device's performance.
Websites like Bestapps2020.com should be avoided, though it should be considered that people usually do not visit them intentionally. It is more likely that a PUA installed on the computer has modified the browser settings to open such pages automatically. Therefore, malware experts recommend scanning affected computers for browser hijackers and similar applications.