Downgrading from Big Sur to Mojave

I upgraded my MacBook Air from Mojave to Big Sur, which I have instantly regretted as 2 of my crucial apps stopped working. Before upgrading I took backup on external drive using Time Machine, which I do regularly anyway. As it seemed very easy to downgrade back to my previous system I started the process of restoring from the Time Machine backup. All seemed to go well, but now 6 hours after I have started restoring I can see no progress at all and the message " Time remaining: Calculating... " but it it does not show any estimated time. The light on external drive is blinking, but I am not sure if it is actually working or is stuck. HELP please!!!