can you go to Dashboard > Settings > Permalinks, make sure the Structure is set to Default. And then Click > Save Changes to rebuild the permalinks. Then retry activating the modules.
Currently, I’m using the Post Name permalink setting. I’m afraid to change if I change this setting, all my blog URLs will change and I’ll lose all my indexed URLs on Google…
While doing this I saw an error in the console. The problem was due to another security module I installed, which blocked the rest API connexion. I deactivated this setting and the Generatepress modules work fine now.