Rebecca Lewis notes a common failure point:
If you upgrade to SQL Server 2025 and your linked servers stop working, you are not alone. This is the single most common post-upgrade failure I am seeing right now, and it hits almost every environment that has linked servers configured from an older version. SQLNCLI is gone. The replacement driver has different defaults. Your connections will fail unless you explicitly tell them how to encrypt.
Read on for the correct solution, the mostly-correct solution, and the solution that a lot of people will take but will probably burn them in a few years.