Its sometimes confusing for people to understand the difference between spoken and written forms when referring to monastics.
Bhikkhunni or Bhikkhu is a descriptive title, indicating our status as ordained Sangha, like priest or bishop. It’s often used in print along with their ordained name in either order; Akāliko Bhikkhu or Bhikkhu Akāliko.
Ayya, Bhante, Venerable, is the ‘style’, i.e mode of address, the way Christian priests are addressed Father So-and-so, or your Grace etc. So we say Ayya Such-and-such when we address a monastic in person or refer to them to others (even online). Referring to them in their absence using Sujato Bhikkhu for example, also occurs but is usually formal. A noticeable exception is the great Bhikkhu Bodhi who is almost universally referred to in this way.
It is considered polite in Buddhist cultures for lay people to refer to monastics either by their title alone (Venerable) or their title and name (Venerable Akāliko) rather than using their name directly. This respectful form is useful for reminding ourselves of the renunciation they have undertaken and their status and role in our society. (and as a monastic I find it also helps to remind me that I am a monk!) Many cultures think referring to someone directly by their first name indicates a familiarity that might not be desirable.
In monasteries, more junior monastics always refer to their seniors using the title, Venerable/Ayya/Bhante/ Ajahn. However, senior monastics may address their juniors using their ordained name only, though many seniors will use the title Venerable out of mutual respect. I rarely refer to myself as ‘venerable’ when I sign off or create a user name, as that seems immodest, but sometimes it’s necessary for monastics to model the correct usage.
There are strict forms of address in traditionally Buddhist countries but westerners are often without this knowledge. In egalitarian Australia, I notice a tendency for people to refer to monastics by their ordained name only without using a style of address - unless you count ‘mate’! There are some monastics, such as Analyo who use their name only, and I know others who think a title is superfluous and creates unnecessary distance. However there is something to be said for a healthy respect for a very old tradition of politeness. Whether this tradition will survive is up to lay people, as I don’t think monastics will insist on lay people addressing them with titles!
Another point is gender. Using the gender neutral Venerable is great to put men and women on equal footing, without needing to identify their gender, or for monastics who consider themselves non-binary. Ven @Vimala recently told me that Ayya can be used for both men and female in Pali, (ayyā for men I think). Some female monastics I know have mentioned that ‘ayya’ is a word for a domestic helper in many Asian countries, so they prefer Venerable. Personally I am glad Theravada has moved on from referring to female monastics as ‘sister’ which implied a lesser status and was too similar to Christian nuns. I’ve heard that some communities are using the hybrid word ‘nunks’ as a non gender specific descriptor and it’s great that Bhante Sujato’s new translations redress the gender imbalance in the suttas through the more inclusive ‘mendicants’ which might have some people reaching for their dictionaries…
Bhante Sujato has expressed his personal preference to be addressed as ‘Bhante’ in this blog post: Bhante or Ajahn? | Sujato’s Blog
But he refers to himself as Sujato Bhikkhu for his work as an author.
Hope this helps!