Is it appropriate to speak to the reader in scientific paper (but without using "you")?
It is not frowned upon and is mostly seen as a stylistic choice. It might be annoying if the same phrase is repeated many times (&quot;Note, note, note, note&quot;). If you prefer an alternative, here are some.
&quot;The reader should note...&quot;
&quot;Readers familiar with XXXX will realise...&quot;
&quot;For those unfamiliar with... an explanation is provided in footnote/ appendix/ section&quot;
&quot;Notably,...&quot;
&quot;It must be stressed that...&quot;
&quot;We emphasise/highlight/note that...&quot;
&quot;It is important to note...&quot;
&quot;Let us note that&quot; - from @user151413
Or simply do not refer to the reader but to the fact.