Steps to reproduce:

1.  Create a new project
2.  Open Project Settings > Editor
3.  Observe "Hide Classic Platforms" toggle state

\\
Actual results: 
"Hide Classic Platforms" option is turned OFF

Expected results: 
"Hide Classic Platforms" option is turned ON

\\
Reproducible with versions: 
6000.4.0b4, 6000.5.0a4

•  This option is ON by default only on one template:

Universal 2D (6.1.4)

• Other core templates have this option turned OFF by default:

Universal 3D (17.0.14)
High Definition 3D (17.0.7)
Mixed Reality (MR) (2.2.2)
VR (9.2.2)
AR Mobile (2.1.2)

Can’t test with versions (the option is not available): 
6000.0.65f1, 6000.3.4f1

\\
Tested on (OS): 
MacOS Sequoia 15.7.3