Index nft create on the linea mainnet blockchain, they are a process who check every 6 seconds new nft events on the blockchain to index it
You can retrieve nft indexed on line blockchain, there histories, metadata ... You have a public api so anyone can consume it. You can filter by owner, address ...
The solution is dedicated for linea main net but you can use it for any evm blockchain I think if you replace the rpc url.
I build the solution in C# on Asp.Net core with the nethereum library, I use infura for rpc and ipfs metadata retrieval, I use metamask sdk to connect user account and see his nfts. The frontend is build with React.js You have a public REST API and you can show endpoint with swagger. The database is postgresSql, the solution is hosted on Azure.