Hi @nicolaslemerle ,
Could you tell me, did you want Unique ID to be generated automatically when a new item created?
I made a sample for you:
Create a list that includes column 'Data' and column 'Id'. 'Data' is a date type column and 'Id' is a text type column.

Create a flow, and I will explain step by step.

When creating a new item, get all items in the list.

Filter the 'Date' column for items in the same year as the new item.
substring(item()?['Date'], 0, 4)
substring(triggerOutputs()?['body/Date'], 0, 4)

Gets the number of filtered items.
Length(body('Filter_array'))

Update the new item.
substring(triggerOutputs()?['body/Date'],0,4)

If the new item has items of the same year, the ID will increase.

If the new item does not have items of the same year, the ID is reset to 1.

Best Regards,
Wearsky