How to merge glass in minecraft?

With the connected glass mod installed, you can eliminate that border and glass blocks or panes will blend with adjacent glass blocks. This allows for a much more seamless and clean design aesthetic.

It works on all sides of the glass blocks or panes so you can create massive glass walls without any borders!

The mod won’t connect any glass blocks that vary in color, unfortunately, but all colored blocks will connect to the same color. There’s also scratched variations of each block and pane if you want to add additional details to certain windows.

And if you want a more pristine look for your glass, this mod offers clear variations as well!

• in the Menu, go to Quality > Connected Textures > Fancy or Fast.
• If that doesn't work, It's probably a texture pack. If your texture pack has a glass texture in it, delete it. It should work then.