AT_Utils VS Kerbalism

Find out what mod needs them, and the dependencies, that's a missing dependency most likely. redownload USI tools, and the USI core perhaps. It needs the community resource pack, and the community category kit, Individual USI modules like the Kolonization may need something else, check each mods dependencies that are clued in to you via errors. AT_Utils could be part of Configurable containers, or another of Tauri's mods, I think this is a library of all of them sort of combined. Find out what installed it. Perhaps try updating or adding it from the Github if you dont have it or have an old build.

There's a known bug where that option doesn't work. But you can disable the notifications for each vessel you launch. https://github.com/Kerbalism/Kerbalism/issues/812

If you want to change up how science works, I'll recommend Kerbalism. Makes it so experiments complete over time, some within minutes and others can take years. It also adds life support mechanics, radiation, and some other stuff.

My all time favorite is Kerbalism. It doesn't make it easier, but I think it makes it more interesting/fun, especially for manned missions. It reworks the science system, and has good life support and ISRU options.

+) someone opened an issue on the GitHub page but his problem isn't the same as mine https://github.com/Kerbalism/Kerbalism/issues/823

For career mode: Kerbalism. Reworked science system that makes it much more interesting, and good life support and ISRU options.

In terms of remaining mostly stock, I'd recommend Kerbalism and Contract Configurator with a few contract packs (second comment has a list) that fit your playstyle.

Install Kerbalism for food/oxygen/radiation/etc.

Adds things such as radiation, and more notably, needs for your kerbals. They need food, water, and air. That and more.