How do I make this less lonely?

You're on one website which should help you (at least in part) accomplish this goal :)

I started to connect to other indie hackers in my city. I personally prefer in-person interactions rather than via zoom for this, and luckily I live in a city big enough to have an IH community. I would suggest the same, or at least to do it virtually.
The other thing I'm trying (but haven't managed yet) is to find an IH mentor to share progress and connect with. Let's see if it works out :)

I think coworking spaces are great for this. Also finding something to do outside of work can be great to meet people. I surf/skateboard/climb regularly and it helps a lot :).

I have the perfect solution for you :) Join the WBE Space it's a virtual space for bootstrappers where we support each other working on our own projects.
We have random coffees, regular events, virtual office, etc...

Those are interesting perspectives, but I'd recommend joining a weekly virtual meetup or something first.

I think reaching out to people on Linkedin and expanding your social network like that can be a really meaningful way to both grow professionally but also just meet like-minded people!

To be honest, I haven't found a concrete solution yet. I actually cleaned up my github issues in hopes to find more engineers to work with my project.

Don't know if anyone will bite.

I personally join every informatics fairs I can find in my country. There are sites such as https://www.eventbrite.com/ or https://www.brella.io/ where you can find events worldwide. Hopefully, these will help you. Also, you can contact me or any other individual in IH. This community is the best I have ever seen. Don't worry be happy. :D

Attend some Meetups! If there are none in your region: become the host of it!

This advises are for myself.

Try not to get sucked into it.
Prioritize your life outside of computer.
Keep indie hacking as just another activity in your life.

Join communities (preferably in-person)! Hold yourself accountable with family and friends. Don’t bother any one person too much haha would definitely recommend finding a mentor

I wouldn’t say indiehackers helped with loneliness. Rather, slack and discord communities where I can get to know people on an individual level are best.

You don’t need a cofounder and you don’t need to give your equity to an incubator

You gotta join a community - you can try out loads of course and join more than one but I run High Signal which has twice weekly Zoom calls - it's been a big help for my mental health

Make yourself available on as many social sites as possible and build an audience on each of them. You will find like minded people there guaranteed.

The right people don't necessarily come from traditional business networking avenues which is why I think social media is useful for this.

Hope this helps!