To load FM23 save games in FM24; first, you'll need to manually move the FM23 save games to FM24.
1. In Desktop Mode, click the folder in the bottom left corner.
2. Under 'Devices' select 'Home'
3. In the top right corner, click on the dropdown menu and make sure 'Show Hidden Files' is ticked
4. Copy the save games you wish to load in FM24: Deck/Local/Share/Steam/steamapps/compatdata/1904540/pfx/drive_c/users/steamuser/Documents/Sports Interactive/Football Manager 2023/Games.
5. Paste the save games to Deck/Local/Share/Steam/steamapps/compatdata/2252570/pfx/drive_c/users/steamuser/Documents/Sports Interactive/Football Manager 2024/Games.
6. Launch FM24 and load the save game as you normally would (the process could take a few minutes).
If you find nothing above helps, please submit a support ticket and our team will try to help.