As a kid, my parents were supportive and would buy me and my little brother a booster pack every now and then, and gift them for birthdays, Christmas, Sinterklaas, when I had good grades, etc.
As an adult, they didn’t care too much. It was just one of the many hobbies and collections I had. The only concern they sometimes had, is whether I wasn’t spending too much. Not because they knew the values of the cards I bought, but mostly because of the 5+ packages that could/would arrive almost every week for certain periods of time.
Also, the times I was excited for a new rare card arrival and they’d ask what I paid for it, I’d usually mentioned halve or 2/3rd of what I actually paid and they thought it was very expensive for a single card (which is of course true ). But since I didn’t spend my money on much else anyway, and I’m an adult who can choose what to spend my own money on, it was still fine, and they were supportive by just not caring too much I guess.
After a few years of collecting, my dad did ask a few times: “Shouldn’t you sell some of your (duplicated) cards?”. As someone who almost never sells cards, but buys almost non-stop, a pretty valid question tbh.
It wasn’t until I sold three cards for 150k USD and used it to buy a house that my parents were a lot more supportive, for obvious reasons. Then again, my dad does still ask “Did you sell some more cards lately?” pretty regularly, and my answer is still mostly the same as most times: "Maybe a few to a fellow Pikachu collector, but that’s about it. I did buy some new cards, though. "
I do buy a lot less cards than a few years ago, though. But my parents don’t even know this. They also didn’t care much when I told them I completed the English portion of my Pikachu collection recently, as one of just two people in the world.
Both of my parents are pretty supportive, and have been supportive since the beginning. Sometimes when I visit my parents I’ll bring my binders just to show my mom all the new things I’ve collected and she gets pretty excited for me. Yeah, it’s cool
Funny thing is in 2020 I got my parents into collecting Pokemon cards…so much so they created an LLC and buy and sell to fund their hobby. They each have their favorite pokemon and both love to hunt singles to buy and grade. It really has brought our entire family closer because of this huge common interest.
My dad would commonly whip out a stack of singles out of his pocket when we are eating out at restaurants for me to check out. Always cracks me up thinking of when my brother and I were young and they couldn’t care less about them back in the day but now thoroughly enjoy them now.
They’re really supportive. My mom took me to events as a kid and then started coming to tournaments in 2007, leading up to her being an organizer for TPCi from 2010-2024. My dad started coming to things around 2022 and he’s done one of the technical sides of the IC and Worlds events for a few years now.
When I talk about values, they go “but it doesn’t matter because you don’t sell things” and I say “yeah but still.”
My parents aren’t really interested in collecting or Pokémon at all. That being said, they aren’t disapproving of my collecting, nor do they shun it in any way. I think they like that I have a hobby that is pretty long lasting and not some “spur of the moment” type of thing. They are more so indifferent I guess, but lean towards supportive. I don’t think they really have a grasp on what I’ve spent though, the value of the cards I currently own, or the sheer amount of time I’ve spent involved in the hobby via things like discord, this forum, YouTube, etc… If I was actually selling cards they would be a bit more interested, but I think anyone would be in that scenario. I actually showed my mom one of my binders briefly the other day. She smiled, but she had no real idea what she was looking at. She actually asked me to show her the cards too.
Both my parents collect things on some level, my dad in way wider scale tho, and they’ve always been very supportive towards my hobby. As a kid my mom often bought me a pack or two when she visited a bigger city and they still give me a gift card in my lgs every christmas and birthday. I’ve sometimes shown some bits and pieces of my collection to them and my mom absolutely loves peaceful park pals. My dad sometimes mentions or implys that i could have a big chunk of money i i sold my collection but i can always pull a reverse card by mentioning his bookshelfs and boxes filled with thousands of books
They think the money could be better spent elsewhere but are overall supportive. My mom even made me a Pikachu crochet tapestry which I will hopefully post in one of my future collection updates.
and they thought it was very expensive for a single card (which is of course true 
). But since I didn’t spend my money on much else anyway, and I’m an adult who can choose what to spend my own money on, it was still fine, and they were supportive by just not caring too much I guess.
Then again, my dad does still ask “Did you sell some more cards lately?” pretty regularly, and my answer is still mostly the same as most times: "Maybe a few to a fellow Pikachu collector, but that’s about it. I did buy some new cards, though. 
"