The .SBFLT files would be in C:\Users\<YOUR_WINDOWS_USER_NAME>\AppData\Roaming\Quest Software\Toad for Oracle\15.1\User Files\
The file may not exist. If it doesn't, there would be no need to change a value there because we don't load public synonyms be default. In that case, you probably have more than 500 private synonyms.
In that case, you can do this instead:
- Start Toad but don't open Schema Browser yet
- Go to main menu -> Session -> Schema Browser Filters
In this dialog you can set the default filters in the Schema Browser - Select Synonyms on the left
- Change settings any way you want to limit the results so that you'll get less than 500 of them. Maybe you want to do "starts with A", or only get synonyms for a certain object type. Whatever works for you is fine.
- hit OK, then open the Schema Browser and go to synonyms. It will be filtered however you configured it for step 4. You can change the filter from the schema browser if you want to.
After you follow these steps, you'll have a file called TOAD_DEF.SBFLT in the folder mentioned above.
Toad version 16.0 will be released on April 26th and this will be fixed. It is already fixed in beta, which you can get now. Get the beta version here.