I'm going to recommend the use of some FREE programs I use to reduce telemetry as much as possible.
O&O ShutUp10: (Only for Windows 10), this is a portable & free program it is good to control many OS options from a single location. Also let you reduce the telemetry, use it after you activate your OS on Win Servers, when using the Home and Pro versions, it doesn't remove anything but deactivate serveral services, and depending on your selections this may interfere with activation, this happened to me, when making a fresh reinstall of 10 on my PC, wich was previously activated by HWID and I learned the lesson the hard way.
W10-Block: Attached on this post, (only for 7 and 8.x). this is a batch file created by abbodi1406, created initially to avoid been updated to 10, that's why the name, but it is good to reduce telemetry, that stsrted to be introduced on this systems updates about the end of 2017, it is recommended to run it after first install and after the OS reboot that follws installing updates.
Firewall App Blocker (Fab) v1.7: (For 7 to 10), this is a portable & free program to easily control the Windows Firewall, if selecting White List it blocks all inbond and outbond trafic, only the executables you allow can connect to Internet, It is very simple but works fantastic, I have several years using it. Just extract it to a folder on the root of the OS and make a link on your prefered location. attached a sample my white list, just put it on same folder and import it, those that are allow for Avast are only to let it download virus definition updates, for Avast program update better allow all the others or temporary disable the white list to let it do it.
Simple Firefox Backup: This is not related to block telemetry, but it is a portable & free program very useful tool to copy all your preferences, saved login password, advertising blocker and its settings, etc. from a user of FireFox to same browser installed on another PC as long as using the same user name.
I know FireFox has this service integrated (sync) but I prefer to keep my personal passwords at home and not on a server that could be hacked.