Music and audio production

Do you know if the CD is the exact same master as the one you have in digital form? Albums from before around 2015 typically have an ever increasing number of releases proportional to their vintage and fame, and often times with different masters. It's a pretty arduous process to tell which release has the best sound quality, often times "remasters" don't necessarily sound better than older mixes. Ideally you would be part of a community that shares as many releases for each album that you care, download/try then all and see which one sounds best. There may be some opinions on the internet of people sharing which release is best for each album that you could rely too, but those are hard to come by.

As rules of thumb, for old artists always try their original release. Try remasters from the 80s and early 90s. Be very suspicious of remasters from the mid 90s all the way to 2015 (loudness wars, discs were made to sound louder instead of better), make sure you compare those to the original releases. Never prefer a vinyl over the best CD release, unless it's something that was released before the 80s and you have actually verified it to sound better than the best CD mix.

For more contemporary artists from the mid 90s to 2015 try to see if they have new releases from after 2015 OR something from a label like mobile fidelity.

Any remaster made by the Mobile Fidelity (Mofi) label is likely good, even from the loudness war period.

It's the master and original source that matters most, an mp3 is fine if it was reasonably encoded, but obviously you ideally want a lossless (flac) encode. Even though mp3 encoders have been fine for the last 20~ years you still encounter botched encodes that are actually multiple generation of reencodes and god knows what. There is a bit of a "prestige" when something is encoded in flac, it's less common for those to be botched but you never know...