Do you know of ways to financially support the Sangha? I wonder what people, groups and projects one can support? 

Both monastic and lay fields are on topic.
The easiest approach would be to find a temple/monastery in the tradition you want to support and go to their website or visit them in real life if possible. Their website often contains details on how to to support them, e.g. via Paypal with a single or monthly donation. Some places also have a "wishlist" with items they need such as toiletpaper, gardening tools, food supplies etc. Other places have projects that they need help with such as a library project or physical buildings that need to be build. Manual labour can be a great way of helping out too.

Many monasteries have a social media page as well, e.g. Facebook where they allow people to make donations.