Can't all expenses be deducted when filing taxes? I mean, taxes are paid on profit, which is revenue minus expenses.

Yeah the person you are replying to was imprecise - there's actually tax credits for R&D expense in the US rather than just tax deductions.

https://www.plantemoran.com/explore-our-thinking/insight/202...

Starting this year you need to amortize the R&D expenses over 5+ years, which is going to be brutal for startups.

Losing a lot of money and you can't write off your engineers

Not to mention the thing about tax credits, but when people say "R&D expenses" they often include quite a lot of investments on their definition.

In fact, it's arguable if anything in R&D qualifies as an expense at all.

Only money spent that turns into an asset is investment. I’m not sure how it is in US, but in Germany, for example, not even registering a patent is an investment and does not imply the creation of an asset — only buying the patent creates the asset.