A new alternative is the Apple AirTag or the Samsung SmartTag (possibly similar systems from other companies exist or will come soon).
These are small tags with Low Energy Bluetooth technology that the smartphone can locate. As they are small (ca. 4x4x1cm) and the battery (CR2032, ubiquitous battery in various items like fitness trackes or kitchen scales) is supposed to last for a year, you can hide one (or several) on your bike somewhere.
If the tag is not within reach of your own phone, then it uses the network of other Apple/Samsung users to locate it. It seems (from reading a couple of reviews) that it takes only a few minutes to locate a tag when it is in a reasonably busy place.
I don't have experience with them yet, but they seem a promising alternative to traditional GPS trackers. I used a traditional GPS tracker for a while but hated the hassle of charging it every few days, and it needed a phone card (a cheap one that was deactivated when I didn't use it for a while). Theses smarttags are much more user-friendly in the sense that you can hide them on the bike and then basically forget about them, only change the battery once or twice a year.
Of course they are less reliable than GPS trackers (which work anywhere and send you a message from wherever there is phone network coverage) as they rely on other phone users passing by, so if the bike is hidden in a shed in a remote location you won't find it. But if it's in a city, they have a good chance of working. And as they are active for many months, this increases the chance that they get found.
Update (thanks to comment from @Renaud): The Apple AirTag (but apparently at the moment not the Samsung SmartTag) has an "anti-stalking" feature that limits its use as a tracker for stolen items (but it is a very important for privacy and to reduce abuse). If I understand correctly (based on an article in the German Heise magazine and an article in Laptop Magazine), it activates when the AirTag is separated from its legitimate user for a certain period (after 8 to 24 hours).
After that period it starts to alert nearby iPhones of their presence and also starts to beep (although the Heise article mentions that it is easy to disable the loudspeaker with a bit of technical skill).
So this means that after a few hours it's likely to be found. And if it starts to beep after just 8 hours, it will be practically useless as it will beep every day when you're at work or at night.
Furthermore, the iPhone app allows you to list any nearby trackers, so a thief would be able to check if your bike has a tracker. Of course not all thieves would be aware of this or even have an iPhone, so I guess it might still have some value, especially if you notice the theft soon and can start tracking within a few hours. Also, if a thief checks for trackers before stealing the bike, they may just leave it alone as it increases their risk, especially if they can only find out that there is a tracker somewhere but not actually find where it is hidden it on the bike.