Log in or Log on? Front-end or Frontend? We continue to understand
Last time we talked about the difference between login and log in. In continuation of the topic - a few nuances, which you asked to tell in the comments.
Log in and Log on
Log in and Log on are synonyms. Log in is used more often (otherwise we would not log in, but log in): ')
Microsoft traditionally writes Log on, and Apple and UNIX write Log in. It all depends on the style guide (style guide).
Council Write Log in, if it does not contradict the style manual.
Front end is an abstraction that provides a user interface.
As for the coherent writing, here is the same situation as with the words email and plugin. The language is changing and some words that were previously written with a hyphen, are increasingly merging together today.
Similarly, back-end, back end and backend.
Council If in doubt, write together. This will not be a serious mistake.