I guess my only option is to switch to a more stable distro such as Debian or SUSE. Manjaro has always been touted as a very light distro, good for old machines, but its instability makes it a no-go.

The choice of distro makes almost no difference w.r.t. performance on old hardware, as long as it's still supported.

The only (real but small) difference is between desktop environments and their choice of default apps (eg. file manager).