1.21.5 and 1.21.6 gradually glitch to the point of becoming unplayable

1.21.6 and 1.21.5 gradually disintegrate, they start by distorting the characters for example in my last session the O was distorted both in the menu, in the chat, in the inventory, any writing then after a while all the blocks and the writings became completely black also this extended to any writing. in a session on a realm the inventory glitched and I started to lag until I exited the realm. from 1.21.4 onwards everything is smooth if I lag often it's because I don't have a good computer.