> On the 6502, you can absolutely access all 64K of memory space with an LDA instruction.
There are two LDA instructions (maybe more, I too am about 40 years rusty). One loads from page 0 only and thus saves the time by only needing to read one byte of address, and the other reads two bytes of addresses and can read from all 64k. In latter years you had various bank switching schemes to handle more than 64k, but the CPU knew nothing about how that worked so I'll ignore them. Of course your assembler probably just called both LDA and used other clues to select which but it was a different CPU instruction.
There are multiple, but indirect indexed (pointer + offset) is only for page zero, but you have two of them, one for X and one for Y (I don't recall the differences anymore).
There are two LDA instructions (maybe more, I too am about 40 years rusty). One loads from page 0 only and thus saves the time by only needing to read one byte of address, and the other reads two bytes of addresses and can read from all 64k. In latter years you had various bank switching schemes to handle more than 64k, but the CPU knew nothing about how that worked so I'll ignore them. Of course your assembler probably just called both LDA and used other clues to select which but it was a different CPU instruction.