EDIT: Apologies. Updated with a link to what gorhill REALLY said:
Manifest v2 uBO will not be automatically replaced by Manifest v3 uBOL[ight]. uBOL is too different from uBO for it to silently replace uBO – you will have to explicitly make a choice as to which extension should replace uBO according to your own prerogatives.
Ultimately whether uBOL is an acceptable alternative to uBO is up to you, it’s not a choice that will be made for you.
Will development of uBO continue? Yes, there are other browsers which are not deprecating Manifest v2, e.g. Firefox.
Firewalled for limiting untrustworthy connections to the computer(public networks, hotels, even work).
apparmor for protecting the kernel and controlling file access to applications. SELinux is also a good option but if you need to load kernel modules, it can take a few minutes to sign and register it. It is automated on redhat systems though.
Other than that, do your research and don’t run random scripts and install random apps.
I wonder why you’re getting downvoted
I don’t know, they’re just security measures you can take. Maybe some personal preference thing. I don’t bother with the app guard thing and SELinux is pretty annoying with my Nvidia graphics card but a firewall is something I always setup.