How to reproduce:
1. Open the Hub
2. Select “New project”
3. Select “Editor Version” from the 2021.X streams
4. Observe the template list

Expected result: there are many different templates including variations of “2D”, “3D” (URP or HDRP), “Mobile”, “VR”, “AR”, etc.
Actual result: there are missing templates

Reproduced with: 3.5.0 (2021.1.0a1, 2021.3.28f1)
Not reproduced with: 3.3.0 (2021.3.17f1), 3.5.0 (2020.2.0b2, 2022.1.0a1, 2022.3.4f1, 2023.1.3f1, 2023.2.0a22)

Reproduced on: Windows 10 (by reporter), Windows 11

Notes:
1. Regressed version is not the Hub version but the Editor version → Regressed version is 3.5.0 (2021.1.0a1)
2. In my case I had only 4 templates - “2D Core”, “3D Core”, “2D URP”, and “com.unity.template.urp-blank”
3. For the 2021.X streams all templates were still available at 2023-06-30