A daily journal is probably going to be one of the most private thing in your life. Because I know for a fact that, doesn’t matter how close you are to me I’m never going to share my journal with anyone but me. If you are able to write digitally right way then it is very much possible to have greater privacy than that you’d get in physical journal. If you dont live alone, then its possible they can sneak into your journal. Even if I trust that person completely I’ll still be more comfortable knowing that he/she cannot access it.
Easy to backup
It might not seem like something that is necessary for you, but for me backups are most important part of a journal. If I cannot read my journal entries 10-20 years into the future, then why bother writting it in the first place? Journals are sonething that I want to keep till the day I die.
You might argue that paper will last longer than lets say your hdd or any kind of digital storage, and you are right. But the problem is that in paper it is harder to copy, and maintain. You would to worry about pages turning yellow, different types of insects harming the paper, or worse some kind of disaster happening (like fire, water etc) and ruining your paper. You would be lose everything at once. Yes sure if you want to go to the extra mile you can make a xerox copy of your journals and it would medigate this problem. But it would easily get expensive as time goes on.
On the other hand if you write digitally it would be so much easier to make backups of your journal. You can copy the containing folder and back it up somewhere else. Or if you are using something like Notion or Evernote they all have some kind of export method. (You should not be using any writting app anyway which does not let you export your data easily.)
There is theoratically no limit to how you would customise your journal. If you do not like a certain program you can always move to another, if you are still not satisfied to all the options you can write your own, well it would take time, but it is possible. Or you can use simple markdown files. With any text editors, let it be simple notepad or vim.
Digital journals are less bulky, you do not need any significant extra space at your home for digital journals. I have my journals from 2018 written digitally and they are just a few megabytes. Granted I do not write everyday and do not include much medias, (they are mostly plain texts with little bit of formatting here and there), it is still very little amount of files.
Easier to write
It is significantly easier to write on keyboard than to use pen or paper. There is usually significant speed benifits, and automation, which I’ll explain on next point.
You can automate things in your digital journal. If you are someone like me who likes to answer questions in form of Journal (ex: What did you do today?), you can make a template of your writting software so that everyday when you open your journal you start from your template instead starting form a blank page. Yes theoritically you can do the same on physical paper too, but it is easier digitally, and much much more advanced. I shall write a blog post about it someday.
Ability to search and reference back
Its easier to search a page or a mention of a specific thing on your journal. If you wrie digitally. You can also reference back your old journals if necessary easily. For example you can have a page that would contain all the days where youn done something X, you can reference that page each time you do the X. I’ts bit advanced stuff, but yes it would be helpful when you look back at the year or the decade.
Physical form of journaling has its advantages there is no doubt about that, but personally I prefer Digital ones. The beauty of digital journalism is that it can be as much complex as you want it to be, it can perfectly as you like it. Given that you are comfortable giving your time and energy to it. If you want a place to dump your brain and trying to lower your screen on time, then maybe you would be better off with physical ones, but for most people I think digital journal is much better than physical ones.