The only detailed (non-Thai) resource on Makruk I could find so far is the book "Thai Chess & Cambodian Chess (Makruk & Ouk Chatrang)" by Gary Gifford. Besides the rules of both games including a dedicated chapter on counting rules with some endgame problems, the largest part of the thin book (<100 pages) is about openings and annotated games.
I think it is a good book to get started with Makruk, since it gives some basic idea of the strategy, but given the limited scope you can of course not expect deep analyses.
One side note: The author claims in several places that it is not possible to checkmate with 3 queens/met even if they cover both colors. This is not the case, and in one case where he even gives a specific position, Stockfish in fact finds a mate in 20 (where the counting rules would allow up to 59 moves).