This looks like an ideal task for Inscape.
It is free, GPL 2.
It runs on Linux.
It's considerably small, 107 MB download size. That's less than half of Affinity Deisgner, a comparable commercial product. So it should fit on older PCs with little disk space available.
The startup time is certainly not very fast, but once started it's ok. It's a program for ...
OBS-Studio / Open Broadcaster Software
Can take multiple Inputs and overlays(video, screen, single, window, audio...)
Cross platform (linux, Mac, Windows)
it is very easy to use and the default settings should be fine in most cases. just add the desired inputs and you are good to go.
Take a look at their website.
OBS-Studio - Open Broadcaster Software##
In OBS you can record pretty much any part of your screen or audio. You can choose options like window, screen etc for video and mic, speakers etc for audio.
By default these all go into the same channel but under Settings>Output you can choose advanced output mode which also allows for multiple audio channels. So ...
There are two that work: One works in 85-90% of government XFA forms (at least from Canada). Here:
https://code-industry.net/masterpdfeditor/ (Note: one I found few work in MS Windows version but not Ubuntu, weird, I've reported it and submitted a link to the sample)
and here is an particle on installing FoxIT Reader on Ubuntu 20 which I'm testing:
Found this one recently, it is working delightfully for me between Microsoft Edge, Google Chrome, Vivaldi, and Firefox, Linux and Windows:
Sorry, should have put this in originally: I have zero affiliation with this product.