I installed Buster 2 weeks ago and wanted to check for updates the other
day but got an error:

E: Repository 'http://raspbian.raspberrypi.org/raspbian buster InRelease'
changed its 'Suite' value from 'testing' to 'stable'
N: This must be accepted explicitly before updates for this repository can
be applied. See apt-secure(8) manpage for details.

Despite the reference it took me a while to figure out I needed to add this
option, once is enough:

$ sudo apt-get --allow-releaseinfo-change update

(then normal upgrade or dist-upgrade without the option). I later saw that
some got an interactive prompt to accept the change but that wasn't the
case for me.

--- SoupGate-Win32 v1.05