A left field suggestion the iPhone SE 5G. He said he loved the iPhone 6, and wants fingerprint reader. He has small hands so a small phone would be a good idea. Water resistance should survive a dunk in a pool.
OK the screen is small with an old school bezels arrangement that feels 10 years out of date but the processor is plenty fast and Apple support is on point. The camera is OK, good enough for a quick snap of the kids, video recording is good too.
I'm still using an iPhone SE 2020 and its nice pocketable handset. It still has a couple of years of support from Apple. I see no reason to change until that support ends. The latest 5G SE has better battery life than my 2020 version but battery replacements aren't that expensive. I was surprised to see I can get my battery replaced are the Apple store for around £40 quid.
If we are to land Linus with a "funny" phone rather than the obvious choices of whatever the latest and greatest Samsung or Apple handset, at least the iPhone SE would meet some if not all of his requirements. In 2023 for a tech savvy techtuber rocking an iPhone SE would be a talking point at least.