The only safe offline installer for .NET on XP SP2 is from (via the Wayback Machine or MSDN archives). A trustworthy modern mirror is MajorGeeks or FileHippo (for legacy software), provided the hash matches Microsoft’s original SHA-1.
Save this file now, because as time passes, even the archival mirrors risk disappearing. Your 2005-era hardware will thank you.
: Microsoft did release a .NET Core 3.1 in 2019, but this is a modern, cross-platform developer tool that is not compatible with Windows XP.
. This unlocks compatibility for .NET Framework 4.0, which many modern "legacy" apps require Microsoft Dev Blogs Language Packs