I also use Posteo, one thing to note though is that Posteo doesn't (and probably won't any time soon) support custom domains. If that doesn't bother you, it's a great choice.
The other alternative I found during my research, which doesn't have that limitation, is mailbox.org.
Adding to what others here have already said, I'd definitely download Signal and see if you can get any people to move from WhatsApp/Telegram/whatever to Signal.
I don't know much about iOS apps, but you could look into more privacy focused YouTube clients, and possibly 2FA clients too (although that's a bit of a controversial topic on iOS AFAIK).
I saw you mention in another comment that you use Amazon Alexa for smart home appliances. Depending on interest in selfhosting / time / motivation to move away from Amazon, you could look into using Home Assistant instead. It even has a Lemmy community: !homeassistant@lemmy.world.
Yep my mistake, I confused ShadowSocks with Cloak.
No clue how that guy is zooming with one finger, but zooming while recording a video on my Pixel 6 works just fine when pinching with 2 fingers.
I've never used a Pro Pixel (so can't comment on telephoto), but I never noticed it if there is one. From just clicking around between ultrawide and 1x on my Pixel 6, it seems fine and if I had to guess I'd say it roughly takes 0.5s to switch.
Indeed, they all use UFS 3.1 (so does the 128 GB Galaxy S23 though). I have never looked at storage type and my Pixel 6 doesn't feel slow in any way.
I have no idea what you mean with the camera, it is one of the best Android cameras out there. This is also true when running Graphene OS, as long as you download the 'Pixel Camera' app from either the Google Play store or APK sites (must download as an APK bundle then!).
AFAIK you nailed the differences between NewPipe and NewPipeX.
As for FairEmail, I've used it for well over a year without paying and it's been great (I plan on buying the pro version soon). It has kind of a pay what you want model, technically you can unlock all features for literally 10 cents.
I'm not that knowledgeable on security for hosting services with external access either, I'm sure there are some great YouTube videos out there.
A Raspberry Pi should be perfectly fine for hosting something like Seafile or Nextcloud though (Nextcloud might be a pain in the butt to host).
DP altmode means being able to output HDMI over your phone's USB-C port, the Pixels are famous for missing that feature. But I believe from Pixel 8 onwards it was added again, if this is important for you you should do your own research on it though.
I'm afraid your best bet here will be using WhatsApp.
Edit:
FindMy (for Android) might also be usable for that, but honestly if you just want it to work I'd still vouch for WhatsApp.
Signal supports a single momentary position, but not live location.
Here's what I use:
For password manager and weather I use the same apps as you.
I run a Pixel with GrapheneOS. I actually also came from Samsung, and for me there are quite a few creature comforts missing that I didn't even think about (eg. Samsung Dex, DP altmode, I really like the One UI Dialer, Miracast, Brightness Slider in notifications, switching recents and back button, headphone jack, SD card slot, ...).
As for the Pixel being worth it, I'm ok with it as I was due for an upgrade anyway (Galaxy S10 -> Pixel 6). I'd recommend, if you value your privacy and are fine with losing some Samsung features, to either go all the way and upgrade to a new Pixel when your S23 gets old / dies or buy a cheap used Pixel (Pixel 6 and 7 currently has pretty decent value) to just test it out.
i use miracast where I can (my TV and Samsung phone support it natively), as it pretty much just works and is a decent protocol. Sadly every phone manufacturer that isn't Samsung seems to have abandoned it right now, but it is still widely supported in TVs. On Linux, there is the app gnome-network-displays (yes it also works on KDE) to cast your screen over miracast.
Miracast is an actual local streaming protocol (closely related to WiFi Direct). For content streaming the only FOSS standard I am aware of is FCast, but sofar it only is implemented in the GrayJay Android app.
Edit: There is also Deskreen for casting a PC screen.
For casting mobile to PC there is also scrcpy.
This isn't really casting, but I often find that an HDMI cable (often paired with a USB-C to HDMI dongle) is the simplest and most reliable way to display a phone screen on another monitor (as long as the phone supports DP altmode).
I really like Pop!_OS, AFAIK it doesn't have any telemetry. It's basically a Ubuntu fork but without the stupid Ubuntu stuff, and they're currently even working on their own Desktop Environment.