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PLA is indeed a bitch to drill and tap because its low melting point and therefore PLA soften and sticks to the drill/tap. So better use PETG I consider the best compromise for FDM.
For permanent assembly, better use self tapping screws for plastic or sheet metal otherwise just threaded brass inserts. No need to buy them, plenty of these in old household appliances, printers, scanners, portable PC. It is all metric M2 M2.5 M3 even M4