Home Assistant can be used as an AIO for smart home devices. I assume OP is referring specifically to home assistant integrations that are privacy friendly such as Z-Wave and ZigBee devices that only communicate to each other locally over radio instead of over the internet to someone else's PC.
I struggled for years trying to find a way to set up door cameras that were secure enough that I can check in remotely. Around 2015, I finally had a solution.
I ended up spending a couple hundred dollars on a wired camera Setup from 2000s that streams to a old desktop. Then spend a couple hundred dollars on a network and software that I can dial in to view the desktop remotely. I also bought a VPN to dial in. Probably about $2k, which is chump change compared to corporation setups.
After three years and constant maintenance at roughly 10 hours a week, I gave up.
Then around 2020, i bought a Eufycam and setup, plugged it in and was up and running without any maintenance for like $200. They got a major security leak a year or two ago. Kinda sucked.
But damn, the tradeoff is so painful. Either strong secure network that costs a lot (time and money), or a insecure off-the-shelf solution that just works.
All this for the convenience of being able to see the mailman walk up to my door.