How can I add a logo in Modern Team Sites?I can't found out any information about it.In documentation it says that it is possible but from where? In settings I can't found that option.
The below is the "official way to go", but at the end is a suggestion to check for a quick logo change.
Modern Team Sites can't be customized through the settings-menu. Instead, to customize Modern Team Sites, you need to upload required files and assets and apply the changes by executing the
ApplyTheme method. To specifically change the logo of a Modern Team Site, you need to use the Groups Graph API and define the logo in there.
There's a suggestion that you can change your logo by accessing the default logo at
Site Assets stored with the name
__siteIcon__.jpg. By replacing this file with an identically named filed you could apply your own logo to the site.
although the page for changing the logo isn't listed in the site settings, it is still there and you can access it directly with its url: https://contoso.sharepoint.com/_layouts/15/prjsetng.aspx
however when you create a Team site with the SharePoint link from the app launcher, it will be attached to a O365 group, and it is the O365 Group logo that will override your site logo
so in order to change the logo go to the Admin center > Groups > and change the logo of your group there
it can take some time to sync to your site (i was able to force the sync by removing the default acronym logoin the prjsetng.aspx)