I have exactly the same problem, so it isn't an issue concerning your account only. This has to be a general bug.

I have the same issue with:
Mario Bros.
Super Mario Bros.
Super Mario Bros. 2
Super Mario Bros. 3

This is still an issue. Pretty annoying, I hope this can be looked into

EarthBound’s missing too.

Anyone know how to fix this?

I really want to add Super Mario Bros. to the owned games list.

This is still a problem and it really should get fixed, we are talking about some of the most important games in history, everybody's gonna want to add them to their library.

The issue seems to be that Galaxy 2.0 collapses under the sheer amount of results from their database when you search for "super mario" or "super mario bros.", and just glitches out. Other Mario searches do work, but they all take a long time to process and sometimes fail to show relevant results.

Well looking that the post still have replies I can add my 2 cents here.
If you really want to have Super Mario Bros 1,2,3... in some way, add the Super Mario All-Stars collection from 1993, I know is not the same, but I think is at close as it gets to solve this annoying bug,

still no fix for this?

I'll raise my hand as someone who wants to add SMB games to my library. The search query must be timing out. Galaxy ops up at the bottom saying, "Sorry, we couldn't load the data. Retry"

Same for me, I cannot add Earthbound and Earthbound Beginnings :/
Hopefully it gets fixed soon...

Temporal fix i guess writing just a part of the game

the speed of search is your network + your Cpu - any other task currently being run in the background

Lol same wtf. Super Mario Bros 1,2 and 3 is not on the list. GOG being GOG i guess it's a bug because they have to be on whatever database.
yeah except look at your own screenshot for the original NES games, they're not there. The world Bros does nothing to the search.

edit: there is a workaround. A way to "manually add any game" so to speak. Add whatever existing game and edit its title, year and icon. Voila. I added SM all stars and edited to be SMB3. No one can stop me. GOG should hire me honestly.

I submitted a ticket through the GOG interface about this months ago, but never heard back. I wanted to use Galaxy to track my entire game collection, but I can't manually add Super Mario Bros. 2 or 3.

The closest I've gotten to tracking it down is by looking in C:\ProgramData\GOG.com\Galaxy\logs\ClientHelper-MainWindow.log. It seems like whenever you run a search with results that should include either Super Mario Bros., Super Mario Bros. 2, or Super Mario Bros. 3, the whole thing bombs out because what Galaxy receives back from IGDB's API for specifically those three games causes it to break:

2021-05-27 16:27:47.743 [Warning][ (0)] [TID 21604][client_renderer]: Send to browser failed with nullptr exception; message: {"Arguments":{"gamesData":[ {"data":{"developers":[ "Nintendo", "Nintendo EAD" ],"genericReleaseKey":"generic_51154290896276641","genres":[ "Adventure", "Platform" ],"isDlc":false,"isVisibleInLibrary":true,"releaseDate":495417600,"releases":[ "nes_24621", "nwiiu_0005000010106E00", "humble_supermariobros_rifftrax", "nes_Super Mario Bros. (JU) [!].zip", "nes_25300373", "nes_3238455931", "nes_Super Mario Bros.", "nes_3337EC46", "nes_Super Mario Bros", "nes_[
\"Super\",
\"Mario\",
\"Bros.\"

Regular working results on these searches don't have that nes_[ part with the single-line entries that begin and end with \" and "\, so it has something to do with what IGDB's API is returning just for these three games and how Galaxy isn't able to read it correctly.

If you search 'Super Mario Bros. 35', it works because it doesn't try to include any of those three games in the results. Likewise if you search 'Super Mario Bros. 4', 'Super Mario World', and so on. So I guess what this needs is an update to Galaxy to better handle results like these three (maybe an adjustment to the API call, or how the results are parsed).

Edit to fix a spelling mistake and clarify the proposed fix.