Adding consecutive unique ID starting from 1 for each distinct set of values

We can use arrays for that:

array_find(
  array_agg(
    $id,
    "ReportID_2"
  ),
  $id
) + 1

With array_agg we have an array of all id grouped by the ReportID_2 values.

Then, array_find gets the position of the current id in the previous array, starting with the position 0.

Finally, we add 1 to get the positions from 1.

Possible solution by means of PyQGIS.

Let's assume there is a point layer called "Layer_B" with it's attribute table, see image below.

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Case 1. When the new "id" has to be assigned in a range of each attribute field (without grouping).

P.S. Many thanks to @J. Monticolo

Proceed with Plugins > Python Console > Show Editor and paste the script below

from PyQt5.QtCore import QVariant

fieldname = "info" #a field which is used as an aggregating factor 
newfieldname = "newid" #a new field that will maintain new ids

layer = iface.activeLayer()
idx = layer.dataProvider().fieldNameIndex(fieldname)

pr = layer.dataProvider()
pr.addAttributes([QgsField(newfieldname, QVariant.Int)])
layer.updateFields()

req = QgsFeatureRequest()
req = req.addOrderBy(fieldname)

attr_old = None

with edit(layer):
    for feat in layer.getFeatures(req):
        attr = feat.attributes()[idx]
        if attr == attr_old:
            i += 1
        else:
            i = 1
        feat[newfieldname] = i
        layer.updateFeature(feat)
        attr_old = attr

Press Run script and get the output that will look like

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Case 2. When the new "id" has to be assigned every time when the value in another attribute field change (with grouping).

Proceed with Plugins > Python Console > Show Editor and paste the script below

from PyQt5.QtCore import QVariant

fieldname = "info" #a field which is used as an aggregating factor 
newfieldname = "newid" #a new field that will maintain new ids

layer = iface.activeLayer()
idx = layer.dataProvider().fieldNameIndex(fieldname)

list_attributes = []

for feat in layer.getFeatures():
    list_attributes.append(feat.attributes()[idx])
    
list_attributes = list(set(list_attributes))

dct = {list_attributes[i]: i + 1 for i in range(len(list_attributes))}

pr = layer.dataProvider()
pr.addAttributes([QgsField(newfieldname, QVariant.Int)])
layer.updateFields()

with edit(layer):
    for feat in layer.getFeatures():
        attr = feat.attributes()[idx]
        for key, value in dct.items():
            if attr == key:
                feat[newfieldname] = value

        layer.updateFeature(feat)

Press Run script and get the output that will look like

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References:

• Free and Open Source GIS Ramblings | PyQGIS 101: Using expressions to compute new field values
• QGIS Python Tutorial: How to Add/Delete Field and Updating Attribute Value
• PyQGIS developer cookbook
• How to read the attribute values using PyQGIS?