This issue occurs due to the game being on Pre-DX9 API's; the maximum game resolution is like 1920x1200 and can't be pushed passed that without some form of shim; if the gepardShield configuration could be updated to whitelist the following three-files it would be possible to run the dgVoodoo2 shim.
D3D8.dll
D3DImm.dll
DDraw.dll
Link to a dgvoodoo2 RO guide: https://forum.talonro.com/topic/22865-ragnarok-2k-or-possibly-even-4k-in-full-screen/
Not entirely sure if this is an easy ask or not but in 2019 2k and 4k monitors are getting common and having the additional screen-space makes for a much more enjoyable RO experience.