That’s weird, I have a laptop that probably even weaker (Pentium 2020M with 4 GB of RAM) that used to run Ubuntu fairly ok until about 4 years ago (but it has a SSD).
It’s now running Manjaro pretty well, just can’t compile some Rust-based apps because it runs out of RAM. 😄 But I get them from Flatpak instead.
If Ubuntu went off the rails during these last few years it’s a pity. Anyway, it should not be indicative of how well Linux runs on such a machine, just try another distro.