I would strongly advice against it.

It seems like you are looking at a PhD like "the diploma to have" but not realizing what a PhD is in practice. Read a lot of what a PhD consist in: At least, expect to be lonely and work a whole lot of hours by yourself without much guidance or external motivation, you are becoming the expert during a PhD, so you will not find a lot of people that can help you when you have a problem. (I don't say that good and knowledgeable advisors do not exist! but they also have a lot to do in 24h a day!)

IMO, nothing prevent you from studying after your work like if you are already a PhD student, give it a try: Take any advanced CS theory book or better, a Math book in your area of interest and work it out until you managed to do most of the advanced exercises.
If you think this is not a healthy/sane life/work balance.. For a lot of people a PhD is not either.
Take your time and be sure to understand everything in the book at its full extent. While you are doing this or after having done a couple of books, take high quality research papers in your field (lots of them are free), and try to understand them, implement them and try to reproduce their results. If you want a PhD in Deep Learning, do not expect that the PhD will consist in implementing a network, testing it, and start again. You may need to understand a lot of information theory, statistics, inference, math theory, etc. Also, for a lot of research level interesting ideas: implementing them is not possible in current frameworks, Expect to make a lot of coding.
In any other research areas, usually (advanced) math is still a requirement: P/=NP kind of stuff in computability, graph theory, formal (type) logic (eg look at the rules for the Julia subtyping system[3] pg. 12), game theory (AI), category theory (for functional PhDs), stochastic calculus for finance, etc.. You don't need to know it all, only the part that are relevant to your interest, but still!

This may take month with long days to finish. but..

If you like this experience, you have two choices: 1) You feel that you are ready to do your research on your own, and in that case you don't need a PhD as you can continue to advance by yourself by taking any resources available. 2) You really need the diploma for whatever reason, give a shot at online universities, or try to find fast-tracks to obtain a master degree. Finally find an advisor that is willing to follow you and find funds for your PhD position.

In any case, after the PhD acceptance is where all the difficulties start: You need to study a lot, learn to master rapidly new material even if it is not the material you like, experiment a lot, report results, publish in high impact journals, review papers, read papers, prepare presentations, give presentations, give lectures, give exercise sessions, find fundings, write proposals, manage students, manage several urgent overlapping deadlines, prepare datasets, long hours, poor salary, etc. Don't expect that the PhD is related in any way to a bachelor/master program in my experience.

And don't think this will never apply to you if you find the right advisor, several studies study the link between a PhD and mental illnesses (~30%) [1][2], this is not exactly related to your capacity to work hard but more to the capacity of managing so many sources of anxiety while still being productive and often lonely.

All in all, this can be an extremely amazing experience or the worst experience in your life depending of your personality and ability to manage your time! I didn't write to discourage you to do it, but try in baby steps what it is like to be a PhD and after that decide for yourself. If you are convinced, find good advisors that are willing to follow you or guide you to a fast track that can suit you before applying!

[1] https://www.sciencedirect.com/science/article/abs/pii/S00487...

[2] https://www.nature.com/articles/d41586-019-03489-1

[3] http://janvitek.org/pubs/oopsla18a.pdf