Welcome!
Lots of changes since the 70's (when I too got the bug):
Vinyl has largely been replaced with digital streaming. CD's were the intermediate step. Tidal and Qobuz provide CD quality subscription services with access to millions of albums that you don't have to purchase or store. The sound quality debate between vinyl and digital still rages but super good vinyl has gotten really elaborate and expensive.
Solid state amplification has largely gone to class D, high efficiency, low heat producing, no heat sinks, small/lightweight although class A and A/B are still popular. My 70 watt mono blocks are 5" x 5" x 2" and barely warm to the touch. Tubes are still around, with the very best sounding like the very best solid state.
The basics behind loudspeaker design has changed little, with materials and understanding of in-room performance improving. In the last 20 years professional studios have moved to active monitors (sophisticated low voltage crossovers feeding single channel amps that each feed individual drivers in a relatively small cabinet). Active monitors are much more accurate, have greater dynamics, extended bass capacity, eliminate speaker cables, and can add digital signal processing for room correction.
That's the highlights.
