Easier said than done, but yes this is very true. It's way too easy to fuck up and touch the wrong account, or sync the wrong data, or otherwise contaminate your personal projects with work.
This. And even if you do have time to let your mind wander you can't actually "do" your hobbies at work. At least for me I can't do any personal programming projects while working or my job will own whatever I do.
I don't even plan to sell anything, I just want ownership of it so I can't even fill my time with that.
Does your 401k allow you to invest in individual stocks? Does it let you invest in an index fund that matches your investment interests?(like one for just tech companies, or just solar companies, etc).
If you’re able to invest from within the 401k, do it. You’ll get tax benefits.
In terms of general advice though, I’d lean on the 401k here and invest in large index funds (total market, or at least tracking the SP500, or target date funds). This assumes you already have a fully funded emergency fund though.