Here's a trap for young players -- and, as I just demonstrated, not-so-young ones too...
The 74LVX logic series' common trait is "low voltage operation, 5V tolerant inputs". They run from a single 3.3V supply, produce the expected full swing output (0 to 3.3V), and accept input levels up to 5V without complaining. So they are convenient to interface 3.3V circuits, say FPGAs, to legacy 5V logic environments. There's the usual set of 74 series logic gates etc., which provide 5V tolerance on all their inputs.
And then there's the 74LVX245, an octal bus transceiver... According to this older ST Micro datasheet, it behaves just like all its siblings:
https://www.st.com/resource/en/datasheet/CD00001340.pdf. But today, only ON Semiconductor (ex Fairchild) makes the LVX series, and theirs are like this:
https://www.mouser.de/datasheet/2/308/MC74LVX245-D-1811198.pdfNotice that little "application note" on the front page?
A Parasitic Diode is Formed between the Bus and VCC Terminals. Therefore, the LVX245 cannot be Used to Interface 5.0 V to 3.0 V Systems Directly.
Cannot?! What the heck -- isn't that the whole reason to exist for this logic family?! Inspection of the "recommended operating conditions" reveals that only the two control lines are 5V tolerant on this particular chip, but the 8-bit bus is not. Guess what -- it's the bus I wanted to interface to the outside world...

From personal experience I can now confirm that the chip does indeed not handle 5V on those inputs well, but will let them raise the 3.3V supply voltage -- thank you very much!
Does anyone happen to know the back story here? Was this chip
meant to perform as one would expect (and as formerly advertised by ST Micro), but Fairchild got the implementation wrong and had to limit its advertised functionality? It's hard to imagine that they intentionally designed such a compromised thing?!
By the way: I did discover the 74
LVC series from TI and Nexperia in the meantime, and am hoping for a happy ending...
Edit: And it seems ON Semi also makes the 74
LCX series, which also fixes this problem.