Caddy automatically sets up certificates for you. Since I don’t want my subdomain to appear in certificate transparency logs, I use a wildcard certificate which requires using a plugin for my DNS provider.

A reverse proxy, in my case Caddy.

I would prefer manually writing each software using butterflies over having snapd installed on my system.

To explain it a bit further: when you move a file/directory on the same mount point, moving the file/directory is essentially just a rename operation, which doesn’t involve copying the data itself and is a very cheap operation. If you move a file/directory across mount points, you need to (recursively) copy the file/directory, copy file metadata and (recursively) delete the old file/directory, which is slow and error-prone.

the hidden “trashbin”, .Trash-$(uid), invented by Ubuntu

This isn’t some “idiotic principle invented by Ubuntu”, it just follows the freedesktop.org Trash specification. For many users, it can be really beneficial, see also the spec’s introduction:

An ability to recover accidentally deleted files has become the de facto standard for today’s desktop user experience.

Users do not expect that anything they delete is permanently gone. Instead, they are used to a “Trash can” metaphor. A deleted document ends up in a “Trash can”, and stays there at least for some time — until the can is manually or automatically cleaned.

Whether an application like Prism Launcher should use the trash can or delete the files directly is an entirely different question.

I never heard of Cozy, but it looks quite nice. The Self-Hosting Documentation ist a bit lacking, but https://github.com/cozy/cozy-stack-compose contains all required information to set it it up yourself.

I originally used Nextcloud, but it has a lot of features not related to file hosting

Cozy seems to be in a similar situation, where file storage is just one of many features that it provides. If you want just files, it might be the best idea to just use any WebDAV Server or something like File Browser.