Welcome back friends after long pause
Use Google Drive directly
To prevent Files by Google from monopolizing the upload and blocking your PDFs from opening, the simplest solution is to use the Google Drive app itself. Open Drive, tap the "+" button, and then choose "Upload" or "Download." This way, Drive manages the transfer without Files' intervention, and you can continue viewing your documents simultaneously.
Disable automatic association
Files by Google is often configured as the default transfer manager. You can limit this behavior by going to Android Settings → Apps → Default apps, and then removing Files from cloud file management. This will allow Drive to resume its primary role, and Files will no longer launch automatically during uploads.
Optimize parallel reading
Finally, to avoid the frustration of being unable to open your PDFs during a transfer, enable reading through another application (for example, Google PDF Viewer or Adobe Acrobat). By setting a default PDF reader, you bypass the Files lock and maintain smooth access to your documents, even if an upload is in progress.