For Buster see here!

Installed using instructions from several posts by Thaddy as follows:

1. Add stretch-backports to sources.list

Create:   sudo nano /etc/apt/sources.list.d/backports.list
Add:      deb http://ftp.debian.org/debian stretch-backports main

Update:   sudo apt-get update

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2.  FPC 3.0.4 and Lazarus 1.8.4 are both in stretch-backports

Use apt or apt-get, need to install with the -t option.
Answer Y to install without verification.

sudo apt-get -t stretch-backports install fpc
sudo apt-get -t stretch-backports install lazarus

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