background writer

Hi community, I was reading about background process, but especially
about Background
writer, I also found an article on this website
https://postgreshelp.com/postgresql-background-writer/. I understood that
the background writer flushed new or modified data from shared buffers to
disk. I also understood that background writer is based on three
features bgwriter,
bgwriter_1ru_maxpages, bgwriter_1ru_multiple. That article said that
bgwriter_1ru_multipler if the value is set to 2, and if incoming buffers
pages are 10, dirty buffers will be cleared until there are 20 buffers
available or until bgwriter_1ru_maxpages. I have several questions. First,
where should be available buffers on disk or shared buffers for applying
bgwriter_1ru_multiple?, second when there is new or modified data is
written in the two places on WAL and shared buffers both same time? and
finally if we increase bgwriter_1ru_maxpage and bgwriter_1ru_multiple will
there fewer files on pg_wal?

--
Ing. Henry G. Cortez