Asking for your manager to clarify the work priorities is a good idea. Stick to that and do no more, no less. Try to care less if they dismiss you. Only put forward opinions, proposals or possible solutions only if specifically asked to, don't volunteer anything.
Once you have the priority list and have looked through it, make any other suggestions you can think of that makes your remaining time easier. For example, propose that you stop attending specific meetings, but giving a valid plausible reason, for example that as you are leaving your time is better spent finishing off existing work or that as you are going, it's better other people's ideas are considered and implemented not yours as you won't be there
Can you simply take a more neutral stance in meetings? So rather than present your opinion or proposal, just suggest options with pros and cons and leave the decision to them. Or when they argue back, point out that whilst it is your view/recommendation, you totally understand if they prefer to do something differently as after all "you won't be here soon and it will be their issue to manage and not my problem anymore" It takes away the opportunity for others to disagree and argue with you just for the sake of it. Plus makes it clear your are stepping back.
Today, I told someone who was arguing with me that 'to be honest, I don't feel strongly about this and it's not my decision to make. Whatever you decide is fine with me, I am just pointing out some of the issues". (I very nearly said 'I don't actually care' but resisted). It was very freeing. Grit teeth, you will get through it!