As far as we know right now we know about the Source 2013 branch which is Source and it includes HL2 (updated), HL2 EP1, HL2 EP2, Portal, CS:S, DoD:S, Half Life 2: Deathmatch, Half Life 2: Lost Coast, Half Life: Source and TF2. In details, TF2 and Portal both use an even further modded branch to make their custom peculiarities work (classes for TF2, portals for huuuuh Portal). Then there's the "Source 1.5" branch which runs L4D, L4D2, Portal 2 and CS:GO. As last, there's HL2 Alyx, Artifact (lol) and Dota 2 which all run on Source 2.Actually there are multiple branches iirc. hl2/hl2ep1/hl2ep2/portal and css use source 2013 branch, portal 2 has its own branch, l4d/l4d2 have their own branch and csgo has its own branch. Half life alex and dota 2 use source 2.
The only Source games we may be able to see running on Switch from Portal's base would be HL2 and its episodes + Lost Coast, HL:S (although pointless) and for a very limited extent DoD:S and CS:S. TF2 wouldn't work.