First thing you are doing wrong is using an old KiCad version. KiCad is progressing quite fast, and there is about a newer version each month. Currently it’s V6.0.10 and updates in the third number are bug fixes and upgrade should always be safe. More about those changes on: Release Notes | KiCad EDA
Second, the g fro drag shortcut should work, but it’s subtle. If you press it while a selection is active, it drags the selection, if you press it on top of a wire, the wire moves (and what is connected gets dragged) If you press it exactly on a corner, then only the corner moves and you can straighten those pesky wires. (There may have been some small changes made for this in between V6.0.4 and V6.0.10).
KiCad V7 is just around the corner, it’s expected around the end of this month and KiCad V7 can drag sections while keeping connections perpendicular. You can already try out KiCad V7.0.0-rc1 by installing “KiCad-Nightly” from the kicad website. It is important to know though that if you save your project in the new version, you can not open it anymore in an older KiCad version.