Just ask if they have made a decission already and eventually what is a planed start date. You may politely explain that your availability slots are filling up

Just ask if they have made a decission already and eventually what is a planed start date. You may politely explain that your availability slots are filling up for upcoming weeks/months. It is normal for projects to be deprioritized. In that case usually all focus is shifted onto something else - that includes decisions and communication effort too.