Remember to thank the developers on XDA. Without them, the Galaxy S3 would have been e-waste years ago. Now go ahead—download, flash, and enjoy Android 10 on your vintage Samsung.
TWRP 3.4.0 or newer Link: https://dl.twrp.me/i9300/twrp-3.4.0-0-i9300.img.tar samsung s3 custom rom android 10 link
: You must have TWRP 3.5.2 or newer installed. Remember to thank the developers on XDA
: A privacy-focused operating system based on Android 10 that has been successfully ported to the S3 Neo. Chrono Monochrome Builds samsung s3 custom rom android 10 link
However, the most important rule is Installing a custom ROM on an older device like the Galaxy S3 (likely the GT-i9300) carries risks.
Generally considered "Alpha" quality; not recommended as a primary "daily driver". Installation Resources