FAQ: Will I still be able to spend all coins with Seraphis, even very old ones?

Yes.

After the hardfork to Seraphis and Jamtis Monero will still support all "flavors" of XMR that existed at some point in time since the beginning of Monero in 2014. All coins will remain spendable, even very old ones that up to 2017 were the result of pre-RingCT transactions with amounts still visible.

No "coin swap" or similar will have to take place in order to introduce Seraphis and Jamtis.