How much TB currently has the largest commercially available ext. Hard drive that is suitable for an older laptop with USB 2?
https://www.pcgameshardware.de/Festplatte-Hardware-255553/News/WD-MAMR-Technik-und-bis-zu-18-TB-Kapazitaet-1272647/
I did not understand the question. Sorry 6
There are enclosures for 2.5 "and 3.5" hard drives to connect as an external hard drive via USB (also 2.0). In this respect, it makes no difference whether "external" or "internal".
The largest HDDs (all 3.5 ", SATA III) which one finds over miser are 16TB large.
Do you need an SSD (very fast, for programs) or an HDD (slow, rather for data).
Otherwise, you can connect any USB 3.0 hard drive to a 2.0 port, then logically white only have the power of a 2.0 port.
Any internal HDD can be adapted to be used with USB 2.0. He does not show, but a 6 is probably far from it!