Played through version "1D". Comments already submitted to Discord as well, but for completeness:

• F1 didn't work in DOSBox and on FreeDOS; changing 'f1' to '1' in main.lua and using the "1" key helped
• No need (IMHO) to stack the F1/lightbulb "ideas" notifications, one is enough
• Maybe combine jump (alt) and swim (up) actions into a single action
• Driller interaction could have more interesting graphics (pia animation, particles)
• Using of jetpack could have more interesting graphics (pia animation, particles)
• Maybe make it more obvious or consistent to use "Enter" for left arrow level portals, and auto-enter portals with right arrow level portals (maybe requiring "Enter" (with a overlay like the lightbulb?) for right arrow level portals could also "fix" the ctrl+z-finishes-level bug?)
• When using Ctrl+Z with multiple Pias/Dinos, sometimes I had the issue that i got stuck and a new save point was created
• In the level with the switches, maybe add an 'idea' (Pia's Ideas) that sometimes one has to backtrack as the level is a dead-end otherwise
• Slowdown on DOSBox with slow machines; fixed by removing the busy wait loop at the end of maindraw() in draw.lua (and also removing the busy wait loop in the ideas screen draw function) -- here it might be good to take the drawing time into account, so that there's no extra slowdown
• When OPL-2 isn't found, there's an error ad the game cannot start -- maybe degrade gracefully or ask the user if they want to enable OPL-2 audio at the start of the game; making the vgm() function in music.lua return early can fix starting the game when no OPL-2 is present
• Slow music playback when using SBEMU with FreeDOS on real hardware (timer-related issues?)

Finished playing through the game, I like what I see so far. Needs some polishing/fine-tuning especially with regard to music playback/detection and timer/frame sync/update/draw performance, but other than that, this is a really enjoyable DOS game / puzzle :)