Yes, you can convert RAID1 to 10. At least in theory, your controller has to support it. Check the system documentation. TrueNAS ought to.

But gradual upgrades in general are rarely supported. The recommendation is always to do a complete array replacement.

https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s18.html

Don’t put important stuff in /tmp. Put it in /opt or something.

What we should be asking is why “selling a product” is no longer a business model.

Because they’re not selling a product, they’re selling an ongoing service. They run the relay servers, and those cost money every month.