I am new to Manjaro and had (1) seemingly random freezing. Then it started (2) going to a black screen immediately after start. I also noticed that the internet speed was in kBaud rather than 100 MBaud - as mentioned elsewhere.
However, I had already set up a separate Admin account - as in Unix days. That did not black screen, since I only made whatever change triggered it in my Standard account. So I deleted my Admin account and remade it with the same password - it found my account picture, but lost all the apps I had chosen. My new Admin account did not (1) freeze or (2) black screen or (3) reduce internet speed. So all was well.
Recently however, when I do some things it now freezes for ages before returning normal service. If I resize a Chrome window it freezes apparently for ever - I have to restart.
So I’m still puzzled, but have no need to try yet another distro. Manjaro is the best I have tried.
Sorry: “… so I deleted my Standard account and remade it with the same password… My new Standard account did not (1)… (2)… (3)…”
As Fabby advises, I have now upgraded the kernel from 5.13 to 5.14 (5.15 is Experimental)
it. No need to post “That worked!” 
