Proton Drive already lets me pick any folder on my PC ("My computer" > Add folders), but that folder stays tied to that one PC. On my other computers it only shows up under Proton Drive > Other computers > [PC name], always at that fixed location, and the PC that added it stays its only owner. The only area shared equally by all computers is My files, so real multi-PC sync means moving my whole folder structure into it, which breaks paths, shortcuts and apps.

Proposal: folder pairs on every computer
1. On any computer, link any local folder (any drive, any path) to a folder in Proton Drive, as today.
2. On another computer, link that same Drive folder to a local folder of my choice, at the same or a different path. If the local folder already holds the same files, compare and reconnect instead of re-uploading or creating a duplicate.
3. Changes made on any linked computer, on the web or on mobile sync both ways everywhere.
4. Per computer and per folder, choose how it's kept: full local copy, on-demand (downloaded when opened), or not synced (still available on web and mobile).
5. Let me turn a folder I already see under Other computers into a linked folder at a path I choose.

Why it matters
- Real folder structures aren't flat: important folders live on different drives, and many apps, scripts and projects depend on fixed paths.
- Junctions and symbolic links aren't a real fix: they get in the way of Windows search, Quick Access and some apps.
- Adding the same folder separately on two PCs creates two independent copies in the cloud: double the storage and no sync between them.
- MEGA, pCloud and the Nextcloud desktop client already let you pair a local folder of your choice with a cloud folder on each computer.

The Windows app already maps other computers' folders on demand under Other computers, so much of the plumbing seems to be there: letting users choose the local path and sync mode of those folders would solve this.

For anyone with more than one PC, this is the missing piece to move everything to Proton Drive and actually use the storage we pay for.

Related ideas that cover parts of this (could be merged):
https://protonmail.uservoice.com/forums/932839-proton-drive/suggestions/51580013--windows-option-to-customize-the-path-of-the-fold
https://protonmail.uservoice.com/forums/932839-proton-drive/suggestions/50703467-allow-creating-folder-pairs-to-sync
https://protonmail.uservoice.com/forums/932839-proton-drive/suggestions/50980891-select-which-folder-to-sync-on-different-devices
https://protonmail.uservoice.com/forums/932839-proton-drive/suggestions/45727027-selective-syncing-of-files-for-mac-linux-windows