I just installed Solus Budgie on a laptop with QHD+ display, and so Budgie automatically scaled to 2x. Despite most things scaling as they should, the Nextcloud client has a miniscule tray icon. Perhaps it has to do with the icons or the Budgie tray, not sure.
Update: qBittorrent also has a tiny icon, so I'm beginning to think the issue may be Qt related. Discord, for example, does not exhibit the issue.