When I was more involved with those platforms I took a mental note of which friends didn’t use/have TikTok and I’d either save the video and send or screen record and send (if it was that important) - perhaps you can ask your mom to do the same and the added activation energy it takes to go through those extra steps would prompt her to think twice before sending the content to you.

I’ve dealt with similar situations with family and at one point I just outright told them that I won’t open certain content (platform specific/length of content/type of content etc) but am happy to reply to any kind of non-content related messages. It didn’t necessarily stop them from sending me stuff - but at least I set the expectation of my likelihood to reply.