I swapped out a light fitting and now other lights around my house won’t work?

Sounds like you have the 3 plate system if there are three cables (3 x twin & earth). With the power turned off, you need to have all the reds/browns connected together (live), all of the earths connected together (CPCs- green & yellow) but only two of the blacks/blues connected together (neutral). The other black/blue will be the switch return and will be "live" when the switch is turned on so unless one of the three has red or brown sleeving, you will not know which is the switch return without testing. If you get it wrong, you will keep tripping the breaker/fuse. Best to contact a qualified electrician

'..yet some of my lights won’t turn on even though I haven’t touched them ?' Yes you have. You altered the circuit without realising it.

It is likely that when you have swapped the new light you may have left out some feeds or neutrals which then go on to feed the other lights in your house which is causing them not to work due to them being disconnected in your new light.

It could be that you have re-terminated the connections wrong and the loop live feed no longer reaches the other lights.

Looks like you have mixed ur connections up whilst transferring over to the new fitting,call an expert.

its a simple mistake, there can be a lot of cables going to pendents/ light fittings and unless you put it back exactly as it was then it will have knock on effects else where. could be loose connection or wrong conductor in wrong terminal.