I only have two accounts, but I can toggle between them by tapping the account name once the menu is open. That may also cycle through multiple accounts if you can reach that more comfortably.

Apparently that is only a metadata issue that should be fixed soon™. The installed app is still k9 https://github.com/thunderbird/thunderbird-android/issues/8478

Curtail is a wrapper around tools like pngquant, jpgoptim and oxipng. In lossless mode it optimizes and reorders e.g the compression tables. I know of no tool that does that for video data and I am not even sure that is feasable. Video is not stored as a simple sequence of images.

As a CLI there is gifsicle or imagemagick.

As a gui maybe gifcurry, tupitube or some other 2d animation tool https://en.wikipedia.org/wiki/List_of_2D_animation_software