If you don't install software made from people that are not align with your ethics there are probably more than just brave.
I'de rather go with Linux Mint Cinnamon or Nobara with their custom GNOME DE
The real downside of brave is the cryptocrap. It is still optional. However the fact that it support the chromium monopoly is also a bad point.
I think you confuse security and privacy. Samsung are pretty secure from what I saw. They are not private at all however. You can debloat it with adb and maybe tools such as Universal Android Debloater.
There is a couple of guide such as this one: https://linustechtips.com/topic/1402380-ultimate-samsung-oneui-debloat-privacy-customization-guide/
I don't have that comparison but here are some resources that critics FlatPak's misleading security
https://whynothugo.nl/journal/2021/11/26/the-issue-with-flatpaks-permissions-model/
FlatPak is not the as secure as everyone think it is.
I block all ads, I rather tips some moneroj or sats to creators, buy some merch, etc. From my point of view giving 5$ to a creator will be more profitable for him/her than watching a hell lot of ads
You can buy the SMS verification for Telegram on sites likes smspool.net using crypt I currencies such as Bitcoin or Monero.