Have you went to sleep during the several days? dandelions should definitely respawn . I believe the general rule of thumb on most resources respawning is 72 hours plus sleeping once. So keep track of your in game days, make sure three days have passed and that you have went to sleep at least once. If doing that does not solve your problem then make sure to include the following information:
1. Platform (Xbox Console, PC Game Pass, PC Steam).
2. Multiplayer or Single Player Game (if multiplayer, can you let them know how many players in total in the game, and their platforms if you know this)
3. Description of issue.