I have all the dlc and it seems there is no way to remove garbage ragnarok. Its such a poor incredible dlc that there was not a single thing i liked about i..

Should be able to uninstall it, but you'll still see items dropping that are in it, you just won't be able to pick them up. Also won't be able to play Runemaster mastery.

Reinstall game from offline installers. Im not sure if it ossible to add offline builds to GOG Galaxy with just few of all DLC. I guess Galaxy anyway start to update game to download missing content.
Or maye there is an option in Galaxy in game settings to disable DLC(s)?

I guess you want to play from Galaxy. Its possible to add offline build as GOG version to galaxy, but im not sure about partial-DLC-support.
100% no DLC is possible for completely offline build - just dont install Ragnarok.

Try clicking on the arrows by Play, go down to Manage installation and then in there choose DLC and untick Ragnarok. That might work.