Alter text in textbox on ItemDataBound

Question

I am trying to alter the text in a asp:TextBox from a DataList with

protected void DataList7_ItemDataBound(object sender, DataListItemEventArgs e)
{
    if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
    {
        TextBox tb = (TextBox)e.Item.FindControl("txtActivitate");
        txtActivitate.Text = "Activitate: " + tb.Text;
    }
        
}

html

<asp:DataList ID="DataList7"
    runat="server"
    Style="width: 100%"
    OnItemCommand="DataList7_ItemCommand"
    OnCancelCommand="DataList7_CancelCommand"
    OnDeleteCommand="DataList7_DeleteCommand"
    OnItemDataBound="DataList7_ItemDataBound"
    DataKeyField="AID">

.......

<ItemTemplate>
    <div class="row no-gutters d-flex justify-content-center">
        <div class="col-sm-12">
            <asp:TextBox ID="txtActivitate" runat="server" Text='<%#Eval("Activitate")%>' class="form-control form-control-sm bg-white" ReadOnly="true" />
        </div>
    </div>
</ItemTemplate>

but the change is not happening to the control "txtActivitate". How it should look like?