If I were you I would maybe take a good amount of time and then start moving them all to your journal/discord page and then delete the ones you don't need to store anymore. That way you're not spending the money on just sd cards for screenshots. Do you have a computer? if you do you could resize them a little save them all in folders and make room on your SD cards that way.
Also, you could try limiting the amount of screen shots you take like chances are you won't be missing anything. There's been tons of times where I think to screenshot something and then don't and now I don't even remember what it was that I wanted to screen shot. I get it though, when the game first came out I took screenshots of EVERYTHING. I don't do a whole lot anymore though since I've pretty much seen everything once before already. Might screenshot if my villagers are doing something really cute. I make a point though, if i want to keep it i send it to my phone or computer and then delete it off my switch to save memory.
The more you screen shot the more work you're racking up so I'd dedicate some time to actually putting them where they need to be then clear some off!