Hi,

I reinstalled rollercoaster tycoon deluxe and now the game starts but in a smaller screensize than before.
Does anybody know how to get the game started in full screen resolution?

As in it is fullscreen but displaying at e.g. 640x480 pixels with black spaces around the side, top and bottom? Or is the error something else?

Are you running a discrete graphics card (if so, AMD or nVidia) or are you on integrated graphics (intel or AMD?)

As I recall, Roller Coaster Tycoon 1 is better at running in a window than a fullscreen application.

This is less relevant to me, because I simply run RCT 1 & 2 via OpenRCT2.

You may find solutions in the threads on the game series forum, like https://www.gog.com/forum/rollercoaster_tycoon_series/how_to_maximize_rct_deluxe_on_win_10 (run in XP or earlier compatibility mode and disable desktop composition / visual themes / optimisations)
Or see https://www.gog.com/forum/rollercoaster_tycoon_series/hack_run_rct_full_screen_at_any_resolution_up_to_1280x1024/page1 and https://www.gog.com/forum/rollercoaster_tycoon_series/help_with_rct_1_widescreen for discussions about hex editing for widescreen resolutions
Or if you want to use it in windowed mode and see whether that may be better, there's a help page from GOG with a specific file to download https://support.gog.com/hc/en-us/articles/360016539673-Rollercoaster-Tycoon-Deluxe-Resizable-window?product=gog

Here is a discussion from another forum, where a few users have found different ways to fix resolution issues: https://www.wsgf.org/phpBB3/viewtopic.php?f=64&t=18816