Looks like beta channel should have it, correct?
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It's because you're not on the latest GrapheneOS release. Please read https://grapheneos.org/releases#about-the-releases and look at the release channel listing there.
The new virtualization functionality (Terminal app) needs changes to work on GrapheneOS and it wasn't part of the initial work of porting to Android 15 QPR2.
Discussion
It's there on the beta, but it crashed before Linux can start, after the setup phase completes.