I personally think that the main problem is bad search optimization. There quite a lot of good answers on Fediverse (Lemmy) but it is nearly impossible to find them via Google or any other regular search engine. And making things worse since Lemmy is Federated it is not easy to implement correct indexing for it. So it makes a lot of questions(Should each instance index only local posts to prevent duplicated search results? What about small instances? Or use some central instance like Lemmy.World? What about different frontends for same instance like Photon or Alexandrite?).
Try Pixel Tablet based on Pixel 7 chipset. All pixel device have easily unlockable bootloader with ability to use AVB on custom ROMs and 7 years of support. You can install GrapheneOS on it which is the best ROM in terms of security & privacy and have all features that LineageOS has (+ sandboxed Google Play). It also support USI 2.0 styluses.
ADB and Android Studio works perfectly with any other Android phone, so I think it is likely not PC issue.
Small files and apps can also be pushhed/installed
I used OnlyOffice via native .deb package. And yes it broke my apt every time and on every update. I managed by manually editing install scripts to make it work. I never used docker before but want give it a try (maybe podman instead).
You can also write your problem and questions to !selfhosted@lemmy.world community, maybe they can help you
I personally think that the main problem is bad search optimization. There quite a lot of good answers on Fediverse (Lemmy) but it is nearly impossible to find them via Google or any other regular search engine. And making things worse since Lemmy is Federated it is not easy to implement correct indexing for it. So it makes a lot of questions(Should each instance index only local posts to prevent duplicated search results? What about small instances? Or use some central instance like Lemmy.World? What about different frontends for same instance like Photon or Alexandrite?).