Change letters to capital, either all letters of just the first in each word

Configuration Frontend
3

I might be missing something, but why do you translate the day in the template to lower case to begin with?
strftime(“%A”) applied to a datetime object will return the day starting with uppercase

{{ now().strftime("%A") | lower }}
=>
{{ now().strftime("%A") }}

or including the state of your sensor

{% set dag = states('sensor.date') |as_datetime %}
{{ dag.strftime("%A")  }}

You btw have sooner or later to work on your template, it’s using the “legacy” format and will throw deprecation warnings with the next release, see Deprecation of legacy template entities in 2025.12