Reference

https://www.ithome.com.tw/news/173851

Situation

# 24H2電腦升級成25H2之後，.net3.5被解除安裝
After upgrading the PC from Windows 11 24H2 to 25H2, .NET Framework 3.5 was uninstalled.

Solution

[1]
# 確認是不是內網的Windows Update Server
Win + R > regedit

[2]
# 將AU改成0 = 啟用自動更新
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU

[3]
# 安裝.net 3.5
Win + R > optionalfeatures > 打勾 ".NET Framework 3.5"

[4]
# 將AU改成1 = 停用自動更新
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU