What you are describing here is fase feeling of security. Many flatpaks have access to your home dir by default. This is already security flushed down the toilet.
Browser is the biggest attack vector nowadays and this is where your accounts reside. Worrying about package manager while not giving a shit sbout bank account seems out of place.
Attacker will steal your browser cookie the same way it does without flatpak.
If you have poor security hygiene and bad habits, flatpak nor anything else will save you.
My greatest achievement in life was running on stable gentoo installation for a month. Then I messed up something and never found the courage to get back to it.
I have just flown too close to the sunโฆ
I just told you about grey variant. Then you took it personally. Dont know who hurt you so much but you have to let go.