[sachdevs]

Wonder if there is any way to separate this from the painting on top

[jacquesm]

Yes, but not non-destructively. This has been done to some paintings where the painting 'underneath' was considered to be far more valuable (either monetary or historically). Personally I think this should never be done but obviously opinions on such stuff differ.

See:

https://artenet.it/en/removal-of-overpaint/

When the chemical properties of overpaint and underlayer are close this can get extremely hairy, removal speeds of a few square centimeters per day are not unheard of, you need to patience of a monk for this sort of thing.

[notjulianjaynes]

Unless I misunderstood the article the self portrait is on the reverse side of the canvas and can't be seen because someone glued cardboard over it.

[jacquesm]

That may make recovery much more tractable depending on the glue used. The cardboard itself is likely not going to pose a big challenge.