Some years ago bitcoin started running into scaling issues. The period between blocks is fixed at 10 minutes and the maximum size of each block is also fixed at 1Mb so the network transaction throughput was quite limited. Because of the limited transaction throughput the fees per transaction increased significantly because miners prioritize the high-fee transactions for inclusion in blocks. Low fee transactions would sit in the mempool until they were stale or dropped.

This limited throughput led to a massive debate amongst the community about how best to scale bitcoin. One side wanted to change the blocksize (either a step-up in size or to use dynamic scaling), and the other main side wanted to keep the block size at 1Mb and implement off-chain scaling (Lightning Network). I won't recount their arguments for/against, or even tell the story of the debate because it would be very long and there was so much shenanigans involved that I would probably struggle to remain neutral. The long and short of it though is that the side that wanted to keep the block size fixed at 1Mb won out and got to keep the Bitcoin (BTC) name while the other side spun out into a fork called Bitcoin Cash (BCH).

Lightning Network has been going on for years, I at least recall reading about it in 2017 when I started looking into bitcoin

The idea of the Lightning Network is to allow transactions to exist on a separate layer where in theory transaction fees don't have to exist. & transactions don't have to wait for the next block. This allows for microtransactions etc. There are some blockchain transaction fees involved in creating channels & resolving disputes