You can schedule a day on which donations are disabled for a project. You will find this setting at the bottom of the edit project page.
If set, the fundraisers for the project will accept donations until the end of the day set.
For example, if set to 2021-12-31, a donation given at 23:59:59 on New Year's Eve will be allowed, but a donation given at midnight will not be accepted.
You can change this setting if you need to later.
Use this setting if you, for example, have competitions or campaigns that need to close down on a given date.
Note: This doesn't finish the project or the fundraisers. To remove a project and the fundraisers from index pages, you still need to close/finish the project, see how to do this here: https://support.betternow.org/755561-Closing-Hiding-or-Deleting-a-project