Which @angular/* package(s) are the source of the bug?

core

Is this a regression?

No

Description

✅ (Working As Intended) Case 1:
INPUT :host ::ng-deep .bleh
OUTPUT .bleh

❌ (Broken?) Case 2:
INPUT :host ::ng-deep :is(button, a)
OUTPUT :is(button, a)[_ngcontent-ng-c1285227165]

Please provide a link to a minimal reproduction of the bug

https://stackblitz.com/edit/stackblitz-starters-ddu2wd?file=src%2Fmain.ts

Please provide the exception or error you saw

No response

Please provide the environment you discovered this bug in (run ng version)

No response

Anything else?

No response