ive seen people stretch out disk space by moving the large, seldomly-accessed blocks/ folder to a separate disk (often slower) then run bitcoind with blocksdir parameter set so you can keep using your old disk alongside an external drive i dont know about btcpayserver or albyhub specifically, but i...

For a core lightning node there is no need of the full chain but access to old blocks can be needed, I use a pruned node with trustedcoin plugin to fallback in case my node pruned the needed blocks

Btcpayserver uses nbexplorer that wants full chain. I think it can be disabled. Bite the bullet and upgrade to 2 or 4 TB SSD. Report back on how to keep your channels open while migrating 😂😂