Pi4 64 bit Rasbian and dependent files....

[bbhflts]

pi@raspberrypi:~ $ sudo apt-get install opencpn
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
opencpn:armhf : Depends: libcurl3:armhf (>= 7.16.2) but it is not installable
Depends: libgtk2.0-0:armhf (>= 2.14.0) but it is not going to be installed
Depends: libwxgtk-webview3.0-0v5:armhf (>= 3.0.2+dfsg) but it is not installable
Depends: libwxgtk3.0-0v5:armhf (>= 3.0.2+dfsg) but it is not going to be installed
Depends: opencpn-tcdata:armhf but it is not installable
Depends: opencpn-gshhs-low:armhf but it is not installable
Recommends: xcalib:armhf but it is not going to be installed
Recommends: opencpn-doc:armhf but it is not installable
Recommends: opencpn-gshhs-crude:armhf but it is not installable
Recommends: opencpn-gshhs-intermediate:armhf but it is not installable
Recommends: opencpn-gshhs-high:armhf but it is not installable
Recommends: opencpn-gshhs-full:armhf but it is not installable
E: Unable to correct problems, you have held broken packages.
pi@raspberrypi:~ $

[bdbcat]

bbhfltts...


What version of RaspiOS is this?


Thanks
Dave

[bbhflts]

pi@raspberrypi:~ $ cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 10 (buster)"
NAME="Debian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

[hreuver]

You could try this to change the line in /etc/apt/sources.list.d/opencpn*.list:

old

deb http://ppa.launchpad.net/opencpn/opencpn/ubuntu bionic main

new

deb [arch-arm64] http://ppa.launchpad.net/opencpn/opencpn/ubuntu bionic main

The other option is:

sudo dpkg --remove-architecture armhf

(and the first question you should ask yourself why you used "dpkg --add-architecture armhf" before)
After changes in sources by either /etc/apt/sources.list.d/ or dpkg --remove-architecture you need to use

sudo apt update
sudo apt install opencpn

PS I assume you use the bionic files instead of buster.

[hreuver]

Just to show the finesse is in the detail:
Upon rereading I saw the change should be [ arch = arm64 ]
(see https://wiki.debian.org/Multiarch/HOWTO)