How to draw a temporary straight grid lines/help line in any angle?

Do you want to be able to snap to this grid, or just use as a visual aid.

Would guides be helpful?  You can create and save guide setups.

You can create a pattern that will fill a layer with a grid.

I have a premade grid that I keep in a CC Library, and I find that useful.

If you can give us more details on how you would like to use this grid, that might help?

Arbitrary guides are not available in photoshop.

You can draw a line with the pen tool or use the polygonal lasso to make a selection then create a work path from the selection. This will give you a path layer that you can later delete.

Hi @mjoakim, welcome to the community!

You can try pressing Ctrl + R to show the rulers. Then, just click and drag from the horizontal or vertical ruler to add a guide to your document. You can move it around to position it wherever you need.

Here's a video that shares more tips: https://adobe.ly/4gKAdYR

Does that help, or were you looking for something a bit different?

Thanks!
Alek