There used to be some great DIY ones on some crafting forums- I just was too lazy to make them. They used neopreen if I remember correctly. Etsy has some fun ones as well. Or just get the basic plain sleeves from Amazon
I've reused sleeves from other laptops before. Except for those neoprene sleeves. Got a couple of those as conference swag & don't care for them at all.
You can find many on Ebay, Amazon, and Aliexpress.... Under $10... Neoprene ones are soft, light and offer protection from scratches; but not from a 10 foot drop! LOL
I haven't checked specifically for the Legion 5I Pro, but skinit.com has a really good selection of skins and sleeves for all types of devices. You might check them out. They also run monthly giveaways if you are interested.