How do you get cheat codes to work?

See this post https://www.gog.com/forum/dragon_age_origins_ultimate_edition/how_do_i_enable_console_command_on_gog_version/post8

You will also need this mod to make what you type visible.
https://www.nexusmods.com/dragonage/mods/1110

I don't use GOG Galaxy, but if you do, just going by this page https://support.gog.com/hc/en-us/articles/360013424697-How-to-set-Launch-parameters-for-game?product=gog
You would just add -enabledeveloperconsole where it says Arguments.
Note* there is a space before the hyphen.
If you are using a US qwerty keyboard, you just press the tilde key to open the console.