Sharing files? Probably. Reliably syncing files without interaction, and especially without requiring a central server? i don't think so.
The truth is, the android app has existed for over 10 years now and it has never been good. It kinda mostly worked for some use cases, but always-on continuous sync on battery wasn't really one of them. And that's been true even before Google justifiably started restricting filesystem access in KitKat(!) 11 years ago.
If you are looking for an Android app that does syncing in the background well, I can highly recommend FolderSync.
SFTP or SMB depending on your computer/server I guess, or any of the supported cloud options of which there are truly plenty. I'm using SFTP for everything.
FolderSync can do "on-demand" very well if you mean that you just want to tap a sync button to trigger it.
KDE Connect is great, but not for this use-case. SyncThing was absolutely the choice for automated syncing of files between Android and PC. KDE Connect just doesn't do that (AFAIK). The two tools serve pretty different purposes.
KDE Connect wasn't really reliable and easy to use while I did. And Syncthing pretty much eliminated the need to use KDE Connect for me. The only extra-feature of KDE Connect was sharing the buffer, and I just paste to Obsidian now instead (any text editor would do, but I don't know anything better, even though I hate it for being closed-source). Maybe slightly less ergonomic than KDE Connect in this regard, but it's negligible. And I don't need to send files, if I can just share files.
In fact, I think I never even connected the phone via USB since I started using Syncthing. Copying/moving to/from shared folder is amazingly both more ergonomic and much faster (I never learned, why moving files to Android device via USB is so insanely slow).
So I really don't know an alternative. It solved pretty much all my phone/PC sync needs. It also enables backuping the important stuff (I don't use Google for that, or course). Dropbox doesn't cut it either. I really don't imagine how would I use my phone w/o Syncthing, it's pretty much essential.
It's all those little convenience features that make KDE Connect a great tool for my needs. It's only the file transfer features of it that don't live up to my needs, but for that we've got SyncThing (and probably tons of other perfectly valid options that I've never tried, too). For continuous file sync / transfer, SyncThing has been just "set it and forget it" simple for me. It just "does the thing" and keeps on doin' it reliably. :)