Okay, here is one way to do that:
One note of caution though: the above technique is subject to a concurrency issue, whereby if you have two or more users adding a record at the same time, then there is a possibility that you could end up with two records having the same ID. So it’s only really suitable if new records are added infrequently.
For high volume usage, the only way that I am aware of to do this and guarantee uniqueness is to delegate the ID assignment to a 3rd party. Either something like Apps Script or an integration tool such as Integromat.