I have had very varying experiences with suggestions (or talking to someone) about these kinds of changes in life and how to deal with them. Most of the times what I have to say has been met with resistance (sometimes even some sort of resentment or confrontation, or a mix of the two). Why is that? No, not because I consider that they thought I was being a jerk or flippant. But because they had considered certain things undoable, or they didn't do them before, and didn't want to change that and hence when I suggested exactly those things to do in life (or in some cases 'not do') it was considered of no use, being repetitive, clichéd. Of course, by saying this as the leading text in my comment it might look like I am saying OP might be that, but I am not saying that. What I am going to say is - in such a case of OP exactly those things help, what many have actually listed below, and that's why they are cliched and repitive (again, because they work), and can be summed up as:

1. Physical activities as a routine

2. Going out (regularly but maybe not as a routine)

3. A physically engaging hobby that involves someone else and something tangible (besides the two mentioned above)

4. Pickup an intellectually engaging hobby (may or may not involve others)

I shall expand a bit on these (but this will mostly be a huge text wall).

By [1], I mean giving your body the physical exercise it literally "requires" (yup, for us humans it's not a choice, but many of the capable us don't do/get that). Gym is the easiest and helps a lot. Better still, pick up a sport - actually, what works best is doing the two, as one helps and accentuates the other.

If someone is looking for a short, readymade "first to try" list, here's one: gym, running, or/and a racket sport.

Very important: if you have the means and money, consider joining a coaching program to begin with. It's a game changer (no pun intended), and that includes a non-"typical gym-bro/gal" gym trainer.

The [2] is not "let's go out" kind of going out - but just physically stepping out (regularly!!) of your house or usual comfort zone spots - for walks, backpacking trips, travels, treks, camping, hiking, window shopping, attending plays, films in cinemas, puppet shows, bookstores, museums, music shows, comedy shows, get those perfect walking leather shoes for yourself and go around the stores trying to find that and be disappointed that the perfect hasn't been made yet (if you find it, then great).. and so on. You get the gist.

The [3] and [4] are somewhat similar, and I wouldn't regurgitate a lot about that. But just a few examples (you pick your own): for [3], learn to play guitar/cello/violin/drum/some shit/explore - do this under a tutor; and for [4]: pickup reading (may or may not be a reading group), world cinema (a cine club maybe), writing literature (for your diary, you don't have to plan to publish; though you can join a group for sharing if you want). Etc.

None of these is going to happen in a day. But you might not want to make these a months-long research and execution project either. Give it a few days to a few weeks. It's perfectly fine to switch, get bored, move from one to another, get frustrated, try something else, something entirely diagonal, and get disillusioned, but keep trying, keep exploring.

Saying it again, try to get trainers/guides/tutors/groups wherever needed or can. If nothing else, it helps with getting good at something in somewhat shorter time and helps you avoid unlearning a lot of basic things later, and since you are older (as in not a kid or teen), this could be a tad bit more productive, especially in sticking with it.

For me, the point of "how to be alone" is very different from "how to be lonely" (which I doubt anyone wants or hopes so, at least I don't). These engagements give you the bare minimum to sufficient human exposure without having to "socialise" and set you up to be perfectly fine being alone, at least in the short term, and slowly opening up paths for you, giving you some road to decide what turns you want to take in life over time and get back hold of things.

(From your story, it's clear I am not from your geography/culture/etc., so if something seems very weird/odd for you, please note where/why it might be coming from.)

Good luck.