Homey doesn't start

Glad it woke up again.

True for (Pro) 2016-2019 models.
The Pro 2023/mini can also be backed op per USB connection to a PC/Laptop/etc., but this needs manual intervention, and Homey will be offline.
It can be a life saver regarding firmware upgrades, because it’ll create a 1:1 copy of your Homey, which makes it possible to downgrade firmware;
This isn’t possible with the backup subscription.

Yes, by restoring a cloud backup from Homey 2016-2019.
This should work flawless, but issues have bern reported with zigbee & z-wave devices.
I guess “patience” is a factor > Those kind of mesh networks need to build themselves from scratch and settle. This can take up to several hours.

Knowledge base article:
https://support.homey.app/hc/en-us/articles/9302284997660-Migrating-from-Homey-Pro-2016-2019-to-Homey-Pro-Early-2023

And here’s a great community topic: