vue项目报错export ‘default‘ (imported as ‘Vue‘) was not found in ‘vue‘ (possible exports: BaseTransition

warning  in ./src/main.js

export 'default' (imported as 'Vue') was not found in 'vue' (possible exports: BaseTransition, BaseTransitionPropsValidators, Comment, DeprecationTypes, EffectScope, ErrorCodes, ErrorTypeStrings, F
ragment, KeepAlive, ReactiveEffect, Static, Suspense, Teleport, Text, TrackOpTypes, Transition, TransitionGroup, TriggerOpTypes, VueElement, assertNumber, callWithAsyncErrorHandling, callWithErrorH
andling, camelize, capitalize, cloneVNode, compatUtils, compile, computed, createApp, createBlock, createCommentVNode, createElementBlock, createElementVNode, createHydrationRenderer, createPropsRe
stProxy, createRenderer, createSSRApp, createSlots, createStaticVNode, createTextVNode, createVNode, customRef, defineAsyncComponent, defineComponent, defineCustomElement, defineEmits, defineExpose
, defineModel, defineOptions, defineProps, defineSSRCustomElement, defineSlots, devtools, effect, effectScope, getCurrentInstance, getCurrentScope, getCurrentWatcher, getTransitionRawChildren, guar
dReactiveProps, h, handleError, hasInjectionContext, hydrate, hydrateOnIdle, hydrateOnInteraction, hydrateOnMediaQuery, hydrateOnVisible, initCustomFormatter, initDirectivesForSSR, inject, isMemoSa
me, isProxy, isReactive, isReadonly, isRef, isRuntimeOnly, isShallow, isVNode, markRaw, mergeDefaults, mergeModels, mergeProps, nextTick, normalizeClass, normalizeProps, normalizeStyle, onActivated
, onBeforeMount, onBeforeUnmount, onBeforeUpdate, onDeactivated, onErrorCaptured, onMounted, onRenderTracked, onRenderTriggered, onScopeDispose, onServerPrefetch, onUnmounted, onUpdated, onWatcherC
leanup, openBlock, popScopeId, provide, proxyRefs, pushScopeId, queuePostFlushCb, reactive, readonly, ref, registerRuntimeCompiler, render, renderList, renderSlot, resolveComponent, resolveDirectiv
e, resolveDynamicComponent, resolveFilter, resolveTransitionHooks, setBlockTracking, setDevtoolsHook, setTransitionHooks, shallowReactive, shallowReadonly, shallowRef, ssrContextKey, ssrUtils, stop
, toDisplayString, toHandlerKey, toHandlers, toRaw, toRef, toRefs, toValue, transformVNodeArgs, triggerRef, unref, useAttrs, useCssModule, useCssVars, useHost, useId, useModel, useSSRContext, useSh
adowRoot, useSlots, useTemplateRef, useTransitionState, vModelCheckbox, vModelDynamic, vModelRadio, vModelSelect, vModelText, vShow, version, warn, watch, watchEffect, watchPostEffect, watchSyncEff
ect, withAsyncContext, withCtx, withDefaults, withDirectives, withKeys, withMemo, withModifiers, withScopeId)

原因是你在vue3的项目中使用了vue2的语法。