What info does a Mobile Browser send to the Web Server

You only get very basic information on the device.

See for example the following sample requests from a Samsung Galaxy S7:

Samsung Browser:

Accept-Language: de-DE,de,en-US,en

User-Agent: Mozilla/5.0 (Linux; Android 8.0.0; SAMSUNG SM-G930F Build/R16NW) AppleWebKit/537.36 (KHTML, like Gecko) SamsungBrowser/9.2 Chrome/67.0.3396.87 Mobile Safari/537.36

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8

Accept-Encoding: gzip, deflate

Chrome:

User-Agent: Mozilla/5.0 (Linux; Android 8.0.0; SM-G930F) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.143 Mobile Safari/537.36

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3

Accept-Encoding: gzip, deflate

Accept-Language: de-DE,de;q=0.9,en-US;q=0.8,en;q=0.7

Firefox:

User-Agent: Mozilla/5.0 (Android 8.0.0; Mobile; rv:68.0) Gecko/68.0 Firefox/68.0

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

Accept-Language: de-DE,de;q=0.8,en-US;q=0.5,en;q=0.3

Accept-Encoding: gzip, deflate

Firefox Klar:

User-Agent: Mozilla/5.0 (Linux; Android 8.0.0) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Focus/8.0.15 Chrome/75.0.3770.143 Mobile Safari/537.36

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3

x-requested-with: 

Accept-Encoding: gzip, deflate

Accept-Language: de-DE,de;q=0.9,en-US;q=0.8,en;q=0.7

As you can see the HTTP headers of some browsers contain the device model and the Android version number and the used browser app.

Note: Other web browsers may send additional headers.