Before migrating to Lemmy, I decided to request a copy of the data Reddit has on me.
To my surprise, the export includes a file ip_logs.csv with a list of all IP addresses that I used to connect to Reddit for the last 3-4 months!!
That seems quite unnecessary.
You’re asolutely right, IP addresses are kind of a grey area since the are needed for lot of troubleshooting and debugging.
Nevertheless, you can always strive to reduce the stored data.
For your application, you wouldn’t even need to store the historic IP adresses, just a rough geo-location and maybe a mobile/landline/whatever-flag and comparing the current login attempt to that. Even saves you some performance by not repeating the geo-lookups everytime.
Implement your failed-login counter separately by account and source IP and you’ve got decent security without linking an account to an IP.