If it physically fits, then it doesn't need to be officially compatible. The officially compatible lists are always out of date anyway, because the pushchair companies don't want to keep buying every single model of every car seat that comes on the market. They have the most up to date models of their own of course, and they tend to buy the best-sellers (so they can boast that their pushchair is compatible with them!). But for example, the Cybex Aton 2 (no longer sold, but on a lot of pushchair lists) and the Cybex Aton 5 (newer) or Cybex Aton T or whatever is the current model, the adapters are basically the exact same! They don't change them when they update the seat design, so if there is a list which lists an older version of a seat you can be reasonably sure that the newer versions will fit also.
The brands which use those adapters are:
Joie (not Juva)
Nuna
Maxi Cosi
Cybex
Besafe
Avionaut
Britax - newer seats from 2021 - not older ones.
Also, of course this only refers to infant carriers and sometimes car carrycots. The larger seats for up to 4/7/12 years are never compatible.
Kiddy seats are often on the list but they went out of business ages ago.
Avionaut are almost never on the lists, because they are a newer/smaller company but highly worth looking at if you can find a local stockist. Brilliant little seats.
If you have the option to check before buying, a physical fit check should be sufficient IMO. This also allows you to look at the angle of the seat, see if it's not too wobbly etc. If the shop has a weighted baby doll to test with, even better. If you do test in a shop, consider buying from that shop even if it's more expensive than online - being able to go back and get RL advice, have a real person to deal with in case of any warranty issues etc is really worth paying an extra £20 or so for, and of course it supports the store to keep going so that you do have that physical location to check seats at.
You should check the car seat in your car too. This will help you see if the angle is OK and how much space you have in the front seat, plus any recline/rotate features can be tested with your car as well. If you plan to get a seat which goes with a modular base and buy the toddler seat later, it's also a good idea to test the toddler seat.