Adding 30 min. to a time in a template

Configuration
1

I’m stuck on stupid simple thing… I want to add 30 min to the next sunset hour as return by “next_setting” attribute from “sun-sun”

These are the templates I’m experimenting with:

{{state_attr("sun.sun", "next_setting")}} --> Returns: 2022-11-07T15:57:14.859394+00:00

{{as_timestamp(state_attr("sun.sun", "next_setting"),default=None) | int }} --> Returns: 1667836634

{{as_timestamp(state_attr("sun.sun", "next_setting"),default=None) | int |  timestamp_custom("%-H:%M", true)}} --> Returns: 16:57 (Correct value)

{{timedelta( minutes = 30).seconds }} --> Returns 1800 (Correct value)

{{as_timestamp(state_attr("sun.sun", "next_setting"),default=None) | int + timedelta( minutes = 30).seconds}} --> Returns 1667838434 (Correct value)

sofar so good. However:

{{as_timestamp(state_attr("sun.sun", "next_setting"),default=None) | int + timedelta( minutes = 30).seconds | timestamp_custom("%-H:%M", true)}}

Returns an error:

TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’

What am I missing here?

2 
{{ (state_attr('sun.sun', 'next_setting') | as_datetime + timedelta(minutes=30)).timestamp() | timestamp_custom("%-H:%M", true) }}