For self-employed, your home office must be used regularly and exclusively as your place of work. The IRS recognizes a de minimis exception to the exclusivity rule. In this case, de minimis means the non-work use is so limited and trivial as to have no material effect on the work use. For example, suppose one bedroom of your home is a home office, and you don't include the closet in your office square footage. The fact that family members have to walk across the floor of the office to access the closet does not, by itself, invalidate the office. This article is a good recap.
https://aronsonllc.com/the-home-office-deduction-nothing-personal-but-exclusive-use-means-exclusive-...
I don't think a single personal thought will disqualify a home office and a single personal email probably would not disqualify a "business-only" personal computer, but the more personal use you have, the farther away you go from exclusive business use. Remember that most taxpayers aren't audited, but if you are audited, it is up to you to prove the deduction is allowable. The IRS does not have to prove you are wrong, you have to prove you are right.
