Since the release of PvZ: GOTY, this bug haven't got fixed yet, and that's really annoying when you don't know how to fix it.
That's pretty easy to fix it, just follow the steps below:
1. Launch your steam
2. Press the three keys "ctrl+ lshift+esc" simultaneously to open the "task manager"
3. Search for "Steam Client Service", right click on it, then left click on "Open folder location"
4. Now go on the steam folder like on the picture below:






5. Once you're on the steam folder, search the "steam.dll" file, when you've found it, copy it by pressing "ctrl+c" simultaneously
6. Now go to your steam library, and search for PvZ: GOTY, right click on it, then left click on properties.
7. Left click on local files, then left click on browse local files.
8. Now paste your file on this folder by pressing "ctrl+v" simultaneously
9. Launch your game

1. Launch your game
2. Go on the options, then check the "3D Acceleration".
3. Now you got your steam overlay back.

The problem is that you can't get the fullscreen when "3D Acceleration" checked even when the "fullscreen" is checked.
If you want the fullscreen, just uncheck the "3D Acceleration".
ATTENTION: YOU CAN'T GET ANY ACHIEVEMENTS BY UNCHECKING IT
So if you want to get achievements, or just the steam overlay, you'll have to play with the "3D Acceleration" checked, so you won't have the fullscreen.

If you are a begginer, you should know that you'll need atleast 5 "sunflowers" in the first line and and something to kill the zombies such as a peashooter in front of the "sunflowers", and you can protect the "shooters" with a "wallnut" in front of them like on the picture below.
















PS: You'll need a second "shooter" to kill the "coneheads zombies" as fast as you kill a normal zombie with an unique "shooter".















To make a game easier, plant the "sunflowers" as fast as possible (if you are fast you can plant 3 of them).



















Then plant a "peashooter" for the first zombie). Then plant a line of "peashooters" or two if you want to kill the "coneheads zombies" faster, now plant a line of "wallnuts"

When you play, you can enter commands to change a little the visual of the game.
I won't show any picture so it will be funnier to test it.
To remove the codes effect, just type the command again.
PS: You need to type the commands in-game (in case of bugs)

Daisies: Zombies push up daisies when vanquished (your tree must be 100feets tall)
Dance: Zombies start dancing (your tree must be 500feets tall)
Future: Zombies wear sunglasses
Mustache: Zombies wear a mustache (gives you an achievement)
Pinata: Zombies heads explodes like pinatas when they die (your tree must be 1000feets tall)
Sukhbir: Not sure of what it does
Trickedout: Change the style of the lawnmowers.

There is a special zombie that you can see only in one level. You need to have played the entire adventure, and re-do it once you see the zombie. You can spoil yourself below.
SPOIL: THE ZOMBIE IS A YETI, AND CAN BE FOUND ONLY ON THE 4-10 LEVEL
By meeting this zombie, you'll get an achievement.

All the credits goes to:
Maverick_Sidious
and
Mederick_Vador

If you like our guide, why not supporting us? :)
https://psteamcommunity.yuanyoumao.com/tradeoffer/new/?partner=337835869&token=y89rUqqT
You don't need to, but I won't say no :)