@snow It is not your client that is causing this, Snow -- but a problem with the instance itself. I have the same limitation if using Pinafore client in my laptop. shows also 500 max, when it should be Qoto's 65,000 characters true limit.
Freemo knows about the problem and plans to fix it soon - but it is going to take some work, will be part of his upgrading the instance to the newer mastodon 4.01 version.
See this for my latest plea for a fix : https://qoto.org/@design_RG/103386034370170964