That’s true if the right side is a flue, but with neither fire brick nor flue liner in evidence, I suspect it’s purely decorative – I’m interpreting OP’s text description to mean that we’re looking at one of two lined flues, and one of two unexpected void spaces he found when removing the cap. I don’t think the void is actually connected to anything, and instead is just decorative, but if I’m wrong and you’re correct, then yeah – there are more serious issues to deal with here

I think you’re okay here – the code requirement about solid or fully-grouted blocks applies to the masonry supporting the flue liner. What you’re looking at in the photo is a decorative brick wrap around the structural portion of the chimney. My main concern would be to ensure that this area is properly capped and sealed so that critters and rainwater can’t get into the cavity and find their way further into your home.

Problem is that if you’re looking for FOSS software outside of the absolute most mainstream use cases, that type of software is the only available option. GIMP and Inkscape have been mentioned but throw FreeCAD into the ring as well. Shotcut and Kdenlive are passable, but don’t quite measure up to the commercial alternatives.

My particular hobby horse is CFD code. OpenFOAM is fantastic from a technical standpoint, but until recently, to actually use it you either had to buy a commercial front-end, or literally write C++ header files to set up your cases. There’s a heroic Korean developer who’s put together a basic but very functional front-end GUI in the last year to change that, but it only covers relatively straightforward cases at the moment.

My first attempt to switch to Linux for my primary desktop was in 2007, and ended when my attempt to run WoW via WINE mostly worked, but had a weird an completely unfixable audio delay.

Proton (and Valve’s efforts on SteamOS and the Steam Deck more generally) have been an absolute godsend for Linux as a usable daily-driver.

Chomated copper arsenate treated wood has been functionally banned in the US since 2003, and replaced with Alkaline copper quaternary or copper azole preservatives, which are generally safe, though I wouldn’t go eating off a plate made from them or anything. The bigger issure with wood foundations is that even when treated they’re necessarily going to have a limited lifespan – wood still degrades from groundwater contact over time without insect or fungal attack, and water will wash the preservative agent out of the wood over time, eventually letting fungus and termites in.

I installed KDE Neon on Friday evening and things were going great, everything was testing well, and Saturday game night with the gang went flawlessly, but this morning the VMWare Horizon Linux client spontaneously decided that it didn’t want to accept mouse input anymore, so after ten minutes of troubleshooting I gave up and booted back into Windows so that I can be productive today.

A battle lost, but the war is not over yet.

With old masonry wall construction, you need to be very careful about how you retrofit insulation to the walls. Insulating the interior makes it very likely that you’ll have moisture-related degradation of the stone and grout making up the wall, as you’re cutting off drying potential from the interior side of the wall. If it’s possible, insulating the exterior is your best option, otherwise you’ll need to be very conscious about selecting vapor-open insulation and finishes on the interior side, which will limit your options considerably. This article from Building Science Corporation goes over some of the details, and offers some options for interior-side retrofits that might not cause the wall to fail down the road.