I do not have any other program to add (the only options i know are already commented by others), there is one more, you can use a keepass (and/or -xc) database as a folder, and dump files, it is not visible in os file manager, but still cross platform and simple enough, but because of nature of how the encryption is done for a keeepass database, for each file added, whole database is updated (if you have a large folder, then that would be a large file saved, and encrypteed, so it can get slow). I do something handrolled, where if i use a regular folder, but all the files added to it are encrypted by pass (that is gpg), this way, files are encrypted, but saved atomically. But this has some downsides. due to simplistic nature of pass, the output file is not given any fancy unidentifiable name like cryptomator (they also do some atomic file encryptions only, but also do file chunking (split file in multiple parts, and encrypt them seperately, helps with prevention of identification of file by its size) and maintain a map (which, well, maps the file to a unidentifiable name).

But what i can say is, it is not much of “added” protection. If you are leaving your system unlocked, and then fear someone will come and check files, then it can potentiall be of help, but if system is locked, and yiu use a secure lock (many systems have locks which either power machine off after certain attempts, or in case they crash (all programs eventually crash), then they also take system down(and this is good, as system is not left unlocked at any point)) or not powered, then normal disk encryyption is enough, even with against a state level adversary. almost no one is breaking encryptions.