I think you're free to give a talk on any topic that you think is relevant to the audience. I've given several seminars while visiting other institutions and assist with organising them at our institute. The topic of a talk is rarely stipulated, although a speaker is usually expected to give a title or abstract ahead of time to promote the talk.
You can take the talk as an opportunity to introduce yourself, your skills, and wider research topics. It does not have to be restricted to the topic you are interested in working on in the future. You can, of course, have private meetings about other topics while you are there. It is up to you alone (and perhaps your co-authors) whether you share unpublished findings. What's most important it to bear in mind the audience and to focus on a few topics to allow enough time to go into detail rather than overloading with information. I think it's safe to assume that most academics have wider interests than what they are currently working on. If they've invited you or shown up to a talk announced about you, then they're interested to hear what you have to present.
You should think about what you want to get out of the talk. Some people give talks much like a conference but seminars can be more informal. If you are an early-career researcher, bear in mind that these may be people that could hire or collaborate with you in the future so do present yourself appropriately. Think about what topics you want to discuss with them afterwards and what you want them to know about your previous work. For some it's a chance to introduce yourself to the rest of the department. For others it's part of your job interview. The talk can be a formality to justify travel funds for other meetings or can be a courtesy to offer do do a talk while visiting. Content varies considerably accordingly.
What's most important is communication with your host who has invited you. If you have any doubts, then contact them. They'll rarely give you any conditions on what to talk about. You don't have to give them details in advance but it is polite to let them know your plans and interests ahead of time. If you give them enough notice, they can make sure that others that may be interested in your talk or meeting with you while you are there are available to do so. Please bear in mind that they may be very busy and need time to make arrangements, especially if they are covering the costs of your visit.