In the "DevBuild" folder you'll find an updated version of the SQLTools++ executable that supports current Oracle versions up to 23c. Please note that you first need to download a complete installation of SQLTools++ (see the other folder 1.21 RC3) and install / unpack the full set of files. Afterwards replace the SQLTools.exe found there with the updated version included in this "DevBuild" download to get the current version.
Please also note that you need a 32 bit Oracle Client for Windows as prerequisite, 64bit Oracle Clients won't do it. This could be a 32bit Windows Instant Client, which could also be extracted in the SQLTools installation directory if you want to keep things simple.
Current 32bit Oracle Windows client versions 19c / 21c should be fine.