How to stop web browsers sending requests on startup

I looked at netstat -nut which starting a new instance of chromium, where the “page to open at startup” was initially set to none, and afterwards with the page set to a localhost page.

I was appalled to see that regardless of this, chromium fired off several requests to google servers/cloud on startup:

netstat -ntup

(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program nam
tcp        0      1 10.2.5.30:54210         192.178.50.35:443       SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:46084         142.250.217.205:443     SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:58174         35.186.247.156:443      SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:60352         192.178.50.35:443       SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:50552         3.233.136.170:443       SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:40388         142.250.217.170:443     SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:37218         185.199.108.153:443     SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:40404         142.250.217.170:443     SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:37212         185.199.108.153:443     SYN_SENT    192152/chromium
tcp        0      1 10.2.5.30:60368         192.178.50.35:443       SYN_SENT    192152/chromium

I also saw some udp dns requests to 8.8.8.8 fly by.

I was even more disappointed to see that brave browser and firefox does the same.

What would be the best way of going about preventing them from doing this on a linux? I was thinking squid proxy perhaps, but I guess they don’t really need to honor that if they don’t want.