If you don't mind the expense, you might want to consider an electric bike; I found them to be just as fun to ride as regular ones. You can set the e-assist level low enough to exert serious effort when you want to, or just turn off the engine entirely, and conversely set it high if you're tired or your knees hurt.
Sorry if you know this, but it may be helpful to others: If cycling gives you joint pains that's sometimes because the bike isn't set up right for you. There are obviously different sizes of bike and also a few different adjustments that can be made to fit your particular dimensions, and not all of them are obvious or easy to get right, so it might be worth taking the bike to a good shop and asking them to set it up to fit you.
I rode to work (20km each way) for six years rain hail or shine.
Hurting knees can be due to riding in too high a gear. Or by riding too far, or not having rest days. Maybe start with Mon Wed Fri and then move to Mon Tue Thu Fri. If the distance is substantial, even MTTF may not be viable. A more efficient bike made a big difference to me (your bike looks quite inefficient, from a cursory glance - heavy, no clip-ons, etc).
One thing for men to watch out for is pressure on the groin area from a too-narrow seat. This can cause lasting damage to nerves and to the prostate.
I found bike lanes useless unless protected in some way (e.g. by raised dividers). Many car drivers bitterly resent bike riders, in part due to bad behaviour by some riders, so you are at risk from cars.
Hurting knees can be due to riding in too high a gear.
Another common mistake is having the saddle height too low, forcing you to bend the leg too much and putting more stress on the knees to move the pedals down. Even a few centimeters (~5cm) can make a big difference, but it will feel strange at the beginning and it take some rides to get completely accustomed to the different movement.
I found a dropper post to be a great help with that. It's much easier to figure out the right height while riding and not having to dismount to adjust it. And anecdotally, it sometimes feels better to adjust it up or down by 5-10 millimeters, maybe due to different clothes or shoes or posture or surface grade.
Note: even the cheapest dropper posts costs around 100 euro (from a cursory Google search). People who aim for cheap bikes often don't consider them. If you can afford it, consider if it would be a small investment into your comfort and longer-term health.
As of this morning, all three of the "not yet" things have changed:
We cancelled events on 3/9
My work implemented recommended WFH starting 3/11
My kids school cancelled starting 3/12
For about a year and a half starting in September 2008, I rode my bike everywhere. I was very into it, in a retrogrouch way. Over time my knees started hurting so I stopped biking. I just tried coming back to it, easing into it so I don't hurt my knees again, and I was surprised at how many things were different:
Bike lanes: my old commute had no bike lanes. Now there are bike lanes almost my entire way. I'm in a slightly different place, biking West Somerville to Kendall instead of West Medford to Fresh Pond, but (a) if I did my previous commute now there's a mixture of bike lanes and a bike path and (b) the bike lines on my new commute didn't exist ten years ago.
More bikes: I didn't used to run into other bike commuters, but now when I stop at a light there's a whole line of us:
Helmets: I got a new cheap helmet (this one) and they've gotten much better. They're easy to adjust to fit, and they stay adjusted. It's possible that fancier helmets like this were around then, but now it's even the cheapest ones.
My work has showers and a bike cage. Possibly this is just me working at a fancier place now?
The biggest thing is that I'd forgotten how much I enjoy biking. It's just really nice, moving along under my own power, being able to go wherever I want, enjoying the sun. I'm pretty much the slowest bike out there, but there's enough traffic during rush hour that I'm still faster than cars, which is also a fun feeling. I don't know if my knees will be up for this long term, so I'll still take it slowly, but I'm happy I decided to try coming back to it!