I get that error using @ton/core:

Buffer is not defined
./node_modules/ton-core/dist/boc/BitString.js@http://127.0.0.1:3000/static/js/bundle.js:49965:1
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./node_modules/ton-core/dist/boc/BitBuilder.js@http://127.0.0.1:3000/static/js/bundle.js:49051:40
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./node_modules/ton-core/dist/boc/Builder.js@http://127.0.0.1:3000/static/js/bundle.js:49989:41
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./node_modules/ton-core/dist/address/contractAddress.js@http://127.0.0.1:3000/static/js/bundle.js:49018:38
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./node_modules/ton-core/dist/index.js@http://127.0.0.1:3000/static/js/bundle.js:53729:44
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./node_modules/ton/dist/index.js@http://127.0.0.1:3000/static/js/bundle.js:61414:14
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./src/hooks/useTonClient.ts@http://127.0.0.1:3000/static/js/bundle.js:809:80
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./src/hooks/useContractWrapper.ts@http://127.0.0.1:3000/static/js/bundle.js:655:90
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./src/pages/home.tsx@http://127.0.0.1:3000/static/js/bundle.js:952:102
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./src/App.tsx@http://127.0.0.1:3000/static/js/bundle.js:18:88
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
fn@http://127.0.0.1:3000/static/js/bundle.js:91982:21
./src/index.tsx@http://127.0.0.1:3000/static/js/bundle.js:873:81
options.factory@http://127.0.0.1:3000/static/js/bundle.js:92324:31
__webpack_require__@http://127.0.0.1:3000/static/js/bundle.js:91718:32
@http://127.0.0.1:3000/static/js/bundle.js:92970:56
@http://127.0.0.1:3000/static/js/bundle.js:92972:12

I tried to install Buffer from git but it’s but it didn’t work. Also I tried edit webpack config like there: How to Polyfill node core modules in webpack 5 but it’s didn’t work too.