Confirming on the minimum intelligence level, without enough intelligence you get an learning malus, like weariness system, towards how fast your character learns as they need more time to understand the difficult concepts in the book. So as you mentioned it is a soft barrier.

Funnily enough I was thinking the other day intelligence is the stat you take to get into the crafting and maintainence aspects of the game and to avoid as much boring sitting and doing nothing sections as I try to make gear and equipment (proficiency training and gain minimum skill requirements to shorten crafting time)

For a restricted challenge playthough , where you don't worry about crafting, it is still possible to do well as there is npc faction stuff that can cover most aspects - food, shelter, armour, weapons, currency and would work well with a nomad playthrough ( your "intelligence" is then your characters instincts and adaptability to a new world instead of using the knowledge of the past to build your future)

As a low int character you cannot read crucial books, even introductory chemistry probably. You have to stumble through your practical experiments, wasting tons of time and hard-to-get ingredients in failed attempts. I think this checks out from both gamist and simulationist perspectives. I mean, even someone really really stupid can learn to accomplish physical tasks (eventually) and we have specifically "applied science" in the game, not abstract theories.

Sorely tempted to ask you to create an Int 4 character and report back to us with you accomplishments, once you do reach the point of cooking up mutagen 😀

You could try play with an illiterate character and with low intelligence then npc training is emulated on how long your character takes to get the knowledge via physical example. Being illiterate a lot of crafting is off the table, including mutagens.

Npc companions do share their recipes and do help with construction if they have the necessary skill so that could be interpreted as them offering advice in construction.

Bionics, if you can reach exodii can install the stuff with good success rate and as bionics is their baby it can be implied it is biotech or tech that is smart enough to learn based off a strict set of instructions. So you can make a case that lockpicking, safecracking and hacking can be AI assisted when installed.

Which then can be used to get past the security for primers and mutagens from labs - or with difficulty, destroying terrain. You wouldn't get what you wanted but it is a path I can imagine a low int character can take.

It is by no means perfect, but I am just trying to think how a low intelligence character could get the high level stuff in a, in my understanding, way of the lore.