We even did a low-level reset (a representative guided me through it) but to his own surprise the malware was still there.
I was out of warranty and I had to pay a sum to get it fixed, which was more expensive than buying a new tablet.
I'm not that extreme, but I did replace my computer once I got back from Kiev. I'd rather not worry about it.
(my father has an android phone and now I suddenly find myself curious about save/restore and how to find malware on his phone)
No - There is no 'easy' way to store/restore the entire phone as I believe Apple does. (I had a miserable day doing this, when my old Pixel started playing up and had to migrate across to a replacement) - and this was best case when I had the two phones next to each other.
Core 'google' stuff seems fine - either all tied to your account (e.g. contacts) or google app data (texts, pictures etc) which can be backed up to cloud, or directly migrated between phones.
What doesn't work is the logins/settings for all the random apps. Some do store on cloud. Some allow manual export/import of settings. Some you're going to have to setup again from scratch.
Back in the day when I did root my phone, TWRP and similar things let you image/restore the whole phone.
That is the true "factory reset", as it's how they were first loaded with software in production. I believe the more widely-known and generic Android reset is merely restoring from an internal partition.
If you look at the storage requirements of an app, you can see it's split between "App Size" and "User Data" (along with a cache).
AFAIK there's no way to actually backup/move the user data without rooting. Now I can see why Google might not want to store all that (and why I might not want them to) - but it's somewhat silly not to have any options.
I think Android phones with the Google Services Framework installed do provide such a way. Alternatively, if you're using a custom ROM (like GrapheneOS on Pixel devices), you can use Seedvault[0] for full backups of your phone. It basically acts as a drop-in replacement of the backup service provided by Google.
That kinda blows my mind.