All saved macros including samples are no more visible.

I downloaded the old version of GSE from:
https://github.com/TimothyLuke/GnomeSequencer-Enhanced/releases/tag/2.6.55
and manually copied the unzipped folders GSE, GSE_GUI, GSE_LDB in the retail/interface/AddOns folder choosing the merge option.

I also tried to delete retail/interface/AddOns/GSE, GSE_GUI, GSE_LDB and redownload the new version of GSE3 from CurseForge but still, no macros are visible, nor the sample macros.

I had a copy of the previous retail/interface/AddOns/GSE, GSE_GUI, GSE_LDB folders when both macros and macro samples were visible, I tried to copy those back but still, nothing is visible anymore.

If I import a new macro it is visible.

Is there any way to get back my old macros from the backup, where are they stored?

No when you installed GSE2.6.55 over 3.0 and logged in GSE2 would have reinitialised and wiped everything. There may still be something in c:\path\to\wow_retail_\WTF\Account\YOURACCOUNTNAME\SavedVariables\GSE.lua.bak <---back up the existing GSE.lua file and rename this one to be remove the .bak But if you have logged in more than once this may have been updated to reflect what you have now.

Actually _retail_/WTF/Account/ACCOUNTNAME/SavedVariables/GSE.lua (same as GSE.lua.bak.zip ) still has all the macros there but still, those are not loaded in GSE which now I have at the latest version 3.0.08.

ok go to GSE's Options - Plugins - Hit the GSE2Library button to reload your GSE2 macros into GSE3

If I do that I still don't see them, but I see the log message of them being loaded in the general chat.
If I run a /reload they are all there.

Thank you.