Hello guys, I have such a problem: I wanted to try to play multiplayer in Battle.net , and in the end, I don't even know what to click. Has anyone had the same problem? How to solve it?

Hi Friend! Welcome! I am not sure why you see no words, but one problem I see is that you did not open your 6112 port. If you would like to play on battle.net with GoG, join our community on discord: https://discord.gg/ADt3TgFuV7. You can also find our stream on Twitch under the name Trogallart. Trogallart streams on weekends around 2-3 pm CET. Also when you join our streams on Twitch we can help you more directly with your issues. You can also post about any issues with GoG on discord under tech-support. We really hope to see you soon! Let me know if you have any questions.

Now I have opened port 6112, but the problem has not been solved in any way. I have already tried reinstalling, but the problem has not disappeared. I have already contacted Blizzard support, but they have not yet responded. Maybe I did something wrong?

Some app inrefier game window by own overlay. Or something like that. Some info available on GOG Support site (but probably for Diablo 1 game - check all blizz related articles).

Also - PCGamingWiki.

Hello there Denchik have you tried using the open sourced ddraw library from here?

https://github.com/CnCNet/cnc-ddraw/releases

This usually fixes most if not all visual glitches that tend to appear on the battle.net client. let us know if it worked.
And yeah for sure if you have troubles making it work you can check my Discord (link in Niko's post), we play this game on battle.net every weekend so maybe you also will find some nice people to play with that way. ;-)

GOG already provide ddraw wrapper. With additional config tool.
This tool cause issue as well - if you try to set it widescreen instead of 4:3. Set by application for fullscreen and keep aspect ratio for scaling image option

http://www.gog.com/forum/diablo/diablo_1_battle_net_empty_text_boxes/post44