Sitecore 10.1 sitecore_master_index taking 19 hours to rebuild

Question

We have migrated from Sitecore 8.2 (solr 6.6.2) to Sitecore 10.1 (solr 8.4).

The rebuild sitecore_master_index in Sitecore 10.1 is taking 19 hours while it used to take less than 2 hours in Sitecore 8.2.

The number of document count of sitecore_master_index in Sitecore 8.2 was 43919 which is jumped to 569279 documents in Sitecore 10.1.

I compared the Sitecore.ContentSearch.Solr.Index.Master.config in Sitecore 8.2 and Sitecore 10.1

Sitecore 8.2

<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <contentSearch>
      <configuration type="Sitecore.ContentSearch.ContentSearchConfiguration, Sitecore.ContentSearch">
        <indexes hint="list:AddIndex">
          <index id="sitecore_master_index" type="Sitecore.ContentSearch.SolrProvider.SolrSearchIndex, Sitecore.ContentSearch.SolrProvider">
            <param desc="name">$(id)</param>
            <param desc="core">$(id)</param>
            <param desc="propertyStore" ref="contentSearch/indexConfigurations/databasePropertyStore" param1="$(id)" />
            <configuration ref="contentSearch/indexConfigurations/defaultSolrIndexConfiguration" />
            <strategies hint="list:AddStrategy">
              <strategy ref="contentSearch/indexConfigurations/indexUpdateStrategies/syncMaster" />
            </strategies>
            <locations hint="list:AddCrawler">
              <crawler type="Sitecore.ContentSearch.SitecoreItemCrawler, Sitecore.ContentSearch">
                <Database>master</Database>
                <Root>/sitecore</Root>
              </crawler>
            </locations>
            <enableItemLanguageFallback>false</enableItemLanguageFallback>
            <enableFieldLanguageFallback>false</enableFieldLanguageFallback>
          </index>
        </indexes>
      </configuration>
    </contentSearch>
  </sitecore>
</configuration>

Sitecore 10.1

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/" xmlns:search="http://www.sitecore.net/xmlconfig/search/">
  <sitecore role:require="Standalone or ContentManagement" search:require="solr">
    <contentSearch>
      <configuration type="Sitecore.ContentSearch.ContentSearchConfiguration, Sitecore.ContentSearch">
        <indexes hint="list:AddIndex">
          <index id="sitecore_master_index" type="Sitecore.ContentSearch.SolrProvider.SolrSearchIndex, Sitecore.ContentSearch.SolrProvider">
            <param desc="name">$(id)</param>
            <param desc="core">sitecore_master_index</param>
            <param desc="propertyStore" ref="contentSearch/indexConfigurations/databasePropertyStore" param1="$(id)" />
            <configuration ref="contentSearch/indexConfigurations/defaultSolrIndexConfiguration">
              <enableReadAccessIndexing>true</enableReadAccessIndexing>
            </configuration>
            <strategies hint="list:AddStrategy">
              <strategy ref="contentSearch/indexConfigurations/indexUpdateStrategies/manual" role:require="ContentManagement and !Indexing" />
              <strategy ref="contentSearch/indexConfigurations/indexUpdateStrategies/intervalAsyncMaster" role:require="Standalone or (ContentManagement and Indexing)" />
            </strategies>
            <locations hint="list:AddCrawler">
              <crawler type="Sitecore.ContentSearch.SitecoreItemCrawler, Sitecore.ContentSearch">
                <Database>master</Database>
                <Root>/sitecore</Root>
              </crawler>
            </locations>
            <enableItemLanguageFallback>false</enableItemLanguageFallback>
            <enableFieldLanguageFallback>false</enableFieldLanguageFallback>
          </index>
        </indexes>
      </configuration>
    </contentSearch>
  </sitecore>
</configuration>

Has anyone faced the issue? Any suggestion would be appreciated.

Thanks in advance