You'll need to paste the following code in your .index file for the saves to be seen by Space Engineers 2 when clicking "Load".

  "Mars_World": {
    "Meta": {
      "DisplayName": "Mars_World",
      "GameVersion": 12023,
      "GameBuildNumber": 33,
      "SaveGameCreationTimeInTicks": 638739522945517431
    },
    "AdditionalData": null
  },
  "World_Earthlike_NoWater": {
    "Meta": {
      "DisplayName": "World_Earthlike_NoWater",
      "GameVersion": 12023,
      "GameBuildNumber": 33,
      "SaveGameCreationTimeInTicks": 638739524572250976
    },
    "AdditionalData": null
  },
  "World_Planet_Verdure": {
    "Meta": {
      "DisplayName": "World_Planet_Verdure",
      "GameVersion": 12023,
      "GameBuildNumber": 33,
      "SaveGameCreationTimeInTicks": 638739519715288436
    },
    "AdditionalData": null
  }