May I ask how GA anonymizes ip address? What algorythm do they have in place as doing sha-x over 4 numbers (0-255 with skipping some) separates by dots is reversable in seconds on average pc and I wouldn't call it anonymization, rather obfuscation.

I am asking this as a friend of mine is having hard time accomplishing exactly that and is really a hard nut to crack, anonymization is by default irreversable and making such algorythm for 4 numbers (actually even less due to known ip address ranges for EU users + reserved ranges) is not simple. You can seed it but that key must remain unknown to google, while this is again getting very hard with javascript. The only way I see is sending all the data to local proxy script, anonymizing the data on your side and then sending it to GA.

I thing that if GA is doing just some hashing, this opens all the sites, using it, to a GDPR responsibility as data controllers including HN. And this can't be hidden under capet (imho) as a "I can't offer service without it" (legitimate interest).