impress choose preset background

Where can I find background presets for my slides? I did it like a month ago but Im afraid they changed it

but Im afraid they changed it

Who is they?

In the sidebar, if you click Master Slides icon, do you not see a range of master slides available for use?

See help on Master slides

In Impress click File > New > Templates to choose from a selection of templates.

they changed it

Did you untick the box that said Show this dialogue box at startup? You can it back by clicking Tools > Options > LibreOffice Impress > General and ticking the box Start with template selection