So, the bare PowerPoint template with a tiny logo on the bottom right looks, well, bare, but you could still say it is professional, sort of. Worse is when you put in a lot of effort and the results do not look good:
- Clashing colours
- Too childish, or too cute for predominantly machine/male investors
- Tacky, cheesy stock images
- Super complex gradients and other template graphics that take over 50% of the slide surface
No format works for an early stage startup investor pitch with a good idea, it will not work in a sales presentation though.